P = 2.686350117820842*10^2406 - 3.509147003769840*10^2403 x^2 +
   2.232334766012457*10^2400 x^4 - 9.23321306009387*10^2396 x^6 +
   2.797063590071589*10^2393 x^8 - 6.628019419459146*10^2389 x^10 +
   1.281285155718557*10^2386 x^12 - 2.080706919967667*10^2382 x^14 +
   2.900600749513771*10^2378 x^16 - 3.529683274215479*10^2374 x^18 +
   3.799572525545543*10^2370 x^20 - 3.657654959609442*10^2366 x^22 +
   3.177358914380688*10^2362 x^24 - 2.509839111095646*10^2358 x^26 +
   1.814625240727776*10^2354 x^28 - 1.207688796217551*10^2350 x^30 +
   7.435446299837606*10^2345 x^32 - 4.253490093370832*10^2341 x^34 +
   2.269657765882891*10^2337 x^36 - 1.133608420161897*10^2333 x^38 +
   5.316334073138192*10^2328 x^40 - 2.347664003997277*10^2324 x^42 +
   9.78698498875831*10^2319 x^44 - 3.860713086508757*10^2315 x^46 +
   1.444181525125296*10^2311 x^48 - 5.132934302120220*10^2306 x^50 +
   1.736544827340320*10^2302 x^52 - 5.601566614600686*10^2297 x^54 +
   1.725478614191356*10^2293 x^56 - 5.082900519602480*10^2288 x^58 +
   1.433830406931773*10^2284 x^60 - 3.878031085948603*10^2279 x^62 +
   1.006838752933342*10^2275 x^64 - 2.511998423431655*10^2270 x^66 +
   6.028870570737217*10^2265 x^68 - 1.393250733667592*10^2261 x^70 +
   3.103089714603463*10^2256 x^72 - 6.666587245054238*10^2251 x^74 +
   1.382638575445950*10^2247 x^76 - 2.770397956252858*10^2242 x^78 +
   5.366842280628789*10^2237 x^80 - 1.005858930607984*10^2233 x^82 +
   1.825072143393833*10^2228 x^84 - 3.207869510983551*10^2223 x^86 +
   5.465159420757082*10^2218 x^88 - 9.02987914428045*10^2213 x^90 +
   1.447724685668347*10^2209 x^92 - 2.253389040532460*10^2204 x^94 +
   3.406776673880169*10^2199 x^96 - 5.005069504865876*10^2194 x^98 +
   7.148720260786071*10^2189 x^100 - 9.93076381228350*10^2184 x^102 +
   1.342300350538044*10^2180 x^104 -
   1.766031989976773*10^2175 x^106 +
   2.262514329562340*10^2170 x^108 -
   2.823472028631675*10^2165 x^110 +
   3.433398530687380*10^2160 x^112 -
   4.069647349352201*10^2155 x^114 +
   4.703474536791501*10^2150 x^116 -
   5.302034601457534*10^2145 x^118 +
   5.831164114332556*10^2140 x^120 -
   6.258630293213825*10^2135 x^122 +
   6.557411618941536*10^2130 x^124 -
   6.708541700709386*10^2125 x^126 +
   6.703098152426357*10^2120 x^128 -
   6.543047641701977*10^2115 x^130 +
   6.240840903503749*10^2110 x^132 -
   5.817849945123738*10^2105 x^134 +
   5.301914007185092*10^2100 x^136 -
   4.724378349510931*10^2095 x^138 +
   4.117052274652728*10^2090 x^140 -
   3.509479115559841*10^2085 x^142 +
   2.926816185721846*10^2080 x^144 -
   2.388492465214735*10^2075 x^146 +
   1.907675036517837*10^2070 x^148 -
   1.491457505406822*10^2065 x^150 +
   1.141602028087492*10^2060 x^152 -
   8.556279254594532*10^2054 x^154 +
   6.280413776807839*10^2049 x^156 -
   4.515326540439904*10^2044 x^158 +
   3.180167907726034*10^2039 x^160 -
   2.194478115710771*10^2034 x^162 +
   1.483853865742252*10^2029 x^164 - 9.83300223305664*10^2023 x^166 +
   6.386617152824788*10^2018 x^168 -
   4.066288654597450*10^2013 x^170 +
   2.538161330896050*10^2008 x^172 -
   1.553400356631517*10^2003 x^174 + 9.32263314135091*10^1997 x^176 -
   5.486951378176007*10^1992 x^178 +
   3.167420751645592*10^1987 x^180 -
   1.793518595659501*10^1982 x^182 + 9.96261698489905*10^1976 x^184 -
   5.429364360014730*10^1971 x^186 +
   2.903165552666326*10^1966 x^188 -
   1.523280393092388*10^1961 x^190 +
   7.843499419670845*10^1955 x^192 -
   3.963668964374835*10^1950 x^194 +
   1.965969276987846*10^1945 x^196 - 9.57152492960029*10^1939 x^198 +
   4.574490289152389*10^1934 x^200 -
   2.146310190307600*10^1929 x^202 + 9.88690722332728*10^1923 x^204 -
   4.471730279011893*10^1918 x^206 +
   1.985938984779357*10^1913 x^208 -
   8.660807588686577*10^1907 x^210 +
   3.709190693138281*10^1902 x^212 -
   1.560103455468367*10^1897 x^214 +
   6.444739988049591*10^1891 x^216 -
   2.614921174621156*10^1886 x^218 +
   1.042162872740786*10^1881 x^220 -
   4.079981202301375*10^1875 x^222 +
   1.569087899814386*10^1870 x^224 -
   5.928203849050795*10^1864 x^226 +
   2.200417896059673*10^1859 x^228 -
   8.024391148585218*10^1853 x^230 +
   2.875159025345020*10^1848 x^232 -
   1.012212697232504*10^1843 x^234 +
   3.501534455222515*10^1837 x^236 -
   1.190248525711444*10^1832 x^238 +
   3.975802300137773*10^1826 x^240 -
   1.305071797366944*10^1821 x^242 +
   4.209984664855359*10^1815 x^244 -
   1.334677953421113*10^1810 x^246 +
   4.158484665287774*10^1804 x^248 -
   1.273410903504800*10^1799 x^250 +
   3.832555857332483*10^1793 x^252 -
   1.133720397800658*10^1788 x^254 +
   3.296336124395826*10^1782 x^256 - 9.42052424742060*10^1776 x^258 +
   2.646343249978066*10^1771 x^260 -
   7.307246483464030*10^1765 x^262 +
   1.983381588790684*10^1760 x^264 -
   5.291900946277332*10^1754 x^266 +
   1.387961871579574*10^1749 x^268 -
   3.578580485948212*10^1743 x^270 + 9.07022441316217*10^1737 x^272 -
   2.259984088022122*10^1732 x^274 +
   5.535776061884918*10^1726 x^276 -
   1.333038444619680*10^1721 x^278 +
   3.155750717810446*10^1715 x^280 -
   7.344512424651015*10^1709 x^282 +
   1.680457453641542*10^1704 x^284 -
   3.780070966485888*10^1698 x^286 +
   8.359561279291154*10^1692 x^288 -
   1.817527358656161*10^1687 x^290 +
   3.885034062551937*10^1681 x^292 -
   8.164455093279046*10^1675 x^294 +
   1.686863009334956*10^1670 x^296 -
   3.426526103596986*10^1664 x^298 +
   6.843069177401753*10^1658 x^300 -
   1.343603626786899*10^1653 x^302 +
   2.593672378394226*10^1647 x^304 -
   4.922466977085678*10^1641 x^306 + 9.18489000822497*10^1635 x^308 -
   1.684953634573095*10^1630 x^310 +
   3.038952248333740*10^1624 x^312 -
   5.388656454536683*10^1618 x^314 + 9.39412399337185*10^1612 x^316 -
   1.610087299983996*10^1607 x^318 +
   2.713049933388496*10^1601 x^320 -
   4.494475002293981*10^1595 x^322 +
   7.319986511537511*10^1589 x^324 -
   1.172057048939555*10^1584 x^326 +
   1.844977753834419*10^1578 x^328 -
   2.855182746212618*10^1572 x^330 +
   4.343834731262068*10^1566 x^332 -
   6.496885750019254*10^1560 x^334 + 9.55268382834428*10^1554 x^336 -
   1.380795113437095*10^1549 x^338 +
   1.962058315283751*10^1543 x^340 -
   2.740743088982950*10^1537 x^342 +
   3.763510693306638*10^1531 x^344 -
   5.080199940292004*10^1525 x^346 +
   6.741017374907996*10^1519 x^348 -
   8.792674582153970*10^1513 x^350 +
   1.127356164004770*10^1508 x^352 -
   1.420820821885134*10^1502 x^354 +
   1.760146039983033*10^1496 x^356 -
   2.143296569804627*10^1490 x^358 +
   2.565267907439039*10^1484 x^360 -
   3.017814628293543*10^1478 x^362 +
   3.489426100729698*10^1472 x^364 -
   3.965601509627411*10^1466 x^366 +
   4.429447174196560*10^1460 x^368 -
   4.862581625296601*10^1454 x^370 +
   5.246292521230257*10^1448 x^372 -
   5.562850387720804*10^1442 x^374 +
   5.796853983427411*10^1436 x^376 -
   5.936466649461109*10^1430 x^378 +
   5.974406125055940*10^1424 x^380 -
   5.908572891940683*10^1418 x^382 +
   5.742241709894746*10^1412 x^384 -
   5.483792133412483*10^1406 x^386 +
   5.146008822434077*10^1400 x^388 -
   4.745032987972388*10^1394 x^390 +
   4.299084750681276*10^1388 x^392 -
   3.827097125901663*10^1382 x^394 +
   3.347403481153394*10^1376 x^396 -
   2.876602725419878*10^1370 x^398 +
   2.428694249104125*10^1364 x^400 -
   2.014533828230008*10^1358 x^402 +
   1.641619181562812*10^1352 x^404 -
   1.314175940961979*10^1346 x^406 +
   1.033486214800720*10^1340 x^408 -
   7.983852739018635*10^1333 x^410 +
   6.058474727899986*10^1327 x^412 -
   4.515886933994255*10^1321 x^414 +
   3.306264081366439*10^1315 x^416 -
   2.377563904131392*10^1309 x^418 +
   1.679237839489421*10^1303 x^420 -
   1.164829767485104*10^1297 x^422 +
   7.935376392911023*10^1290 x^424 -
   5.308987593571449*10^1284 x^426 +
   3.488020119181430*10^1278 x^428 -
   2.250365276668083*10^1272 x^430 +
   1.425663994840285*10^1266 x^432 -
   8.868588727457016*10^1259 x^434 +
   5.416861600574322*10^1253 x^436 -
   3.248472892534088*10^1247 x^438 +
   1.912630590577480*10^1241 x^440 -
   1.105566862790935*10^1235 x^442 +
   6.273680133767686*10^1228 x^444 -
   3.494815112791049*10^1222 x^446 +
   1.911046205638163*10^1216 x^448 -
   1.025754985147126*10^1210 x^450 +
   5.404076674469516*10^1203 x^452 -
   2.794372932035669*10^1197 x^454 +
   1.418114933715901*10^1191 x^456 -
   7.062874953045376*10^1184 x^458 +
   3.452018055249632*10^1178 x^460 -
   1.655633070050951*10^1172 x^462 +
   7.791700607210830*10^1165 x^464 -
   3.597947165977340*10^1159 x^466 +
   1.630078374010770*10^1153 x^468 -
   7.245523475293265*10^1146 x^470 +
   3.159472661882223*10^1140 x^472 -
   1.351507717181499*10^1134 x^474 +
   5.670960942548448*10^1127 x^476 -
   2.334014989068994*10^1121 x^478 + 9.42179591677835*10^1114 x^480 -
   3.730100770024781*10^1108 x^482 +
   1.448230016133533*10^1102 x^484 -
   5.513881785888662*10^1095 x^486 +
   2.058508315152457*10^1089 x^488 -
   7.535202490236606*10^1082 x^490 +
   2.704305337139761*10^1076 x^492 - 9.51493645106292*10^1069 x^494 +
   3.281827862724674*10^1063 x^496 -
   1.109571526718667*10^1057 x^498 +
   3.677001052421732*10^1050 x^500 -
   1.194262986031659*10^1044 x^502 +
   3.801388459062310*10^1037 x^504 -
   1.185736943005922*10^1031 x^506 +
   3.624144340194998*10^1024 x^508 -
   1.085326295119428*10^1018 x^510 +
   3.184336690499094*10^1011 x^512 - 9.15265315360722*10^1004 x^514 +
   2.576970104042530*10^998 x^516 - 7.106741460354884*10^991 x^518 +
   1.919527070100305*10^985 x^520 - 5.077428255070817*10^978 x^522 +
   1.315169795939462*10^972 x^524 - 3.335572468709188*10^965 x^526 +
   8.282680296727712*10^958 x^528 - 2.013465565926689*10^952 x^530 +
   4.791268546923877*10^945 x^532 - 1.115961983238396*10^939 x^534 +
   2.543898714625890*10^932 x^536 - 5.674924283553106*10^925 x^538 +
   1.238761877862649*10^919 x^540 - 2.645697031412988*10^912 x^542 +
   5.528066528310169*10^905 x^544 - 1.129907715451902*10^899 x^546 +
   2.258937772190814*10^892 x^548 - 4.416838093793809*10^885 x^550 +
   8.445361906230247*10^878 x^552 - 1.578983472142473*10^872 x^554 +
   2.886301523822343*10^865 x^556 - 5.157772274030366*10^858 x^558 +
   9.00927447280871*10^851 x^560 - 1.538065326188156*10^845 x^562 +
   2.566057844702199*10^838 x^564 - 4.183246440184080*10^831 x^566 +
   6.662906363258365*10^824 x^568 - 1.036726908534393*10^818 x^570 +
   1.575657490425618*10^811 x^572 - 2.338846202524272*10^804 x^574 +
   3.390226688499028*10^797 x^576 - 4.798296448841429*10^790 x^578 +
   6.630097417686452*10^783 x^580 - 8.942720476487491*10^776 x^582 +
   1.177274957509828*10^770 x^584 - 1.512465267645572*10^763 x^586 +
   1.895972649294613*10^756 x^588 - 2.318765940004212*10^749 x^590 +
   2.766292480448929*10^742 x^592 - 3.218791725652668*10^735 x^594 +
   3.652393804987598*10^728 x^596 - 4.040989068586522*10^721 x^598 +
   4.358706025852007*10^714 x^600 - 4.582693468544262*10^707 x^602 +
   4.695803111075273*10^700 x^604 - 4.688741559807496*10^693 x^606 +
   4.561319881825257*10^686 x^608 - 4.322569644411743*10^679 x^610 +
   3.989688936013741*10^672 x^612 - 3.585988266929982*10^665 x^614 +
   3.138177945893562*10^658 x^616 - 2.673437612187067*10^651 x^618 +
   2.216715896777711*10^644 x^620 - 1.788627818060961*10^637 x^622 +
   1.404174500186407*10^630 x^624 - 1.072341751792931*10^623 x^626 +
   7.964800475641478*10^615 x^628 - 5.752587779349611*10^608 x^630 +
   4.039372861699552*10^601 x^632 - 2.757027740769818*10^594 x^634 +
   1.828763089939277*10^587 x^636 - 1.178620216644649*10^580 x^638 +
   7.379038749201475*10^572 x^640 - 4.486862605957440*10^565 x^642 +
   2.649162740835810*10^558 x^644 - 1.518452940120143*10^551 x^646 +
   8.447396286832695*10^543 x^648 - 4.560087893863542*10^536 x^650 +
   2.388087569454717*10^529 x^652 - 1.212968867012339*10^522 x^654 +
   5.973994622973118*10^514 x^656 - 2.852244673191626*10^507 x^658 +
   1.319787541596352*10^500 x^660 - 5.917012482879806*10^492 x^662 +
   2.569599033701511*10^485 x^664 - 1.080620010752694*10^478 x^666 +
   4.399494748327280*10^470 x^668 - 1.733520668334456*10^463 x^670 +
   6.608801006599677*10^455 x^672 - 2.436976545587831*10^448 x^674 +
   8.689185240682283*10^440 x^676 - 2.994787739224995*10^433 x^678 +
   9.97398312034905*10^425 x^680 - 3.208772811716005*10^418 x^682 +
   9.96838679970145*10^410 x^684 - 2.989300706409979*10^403 x^686 +
   8.649909540838832*10^395 x^688 - 2.414260480021974*10^388 x^690 +
   6.497036542475437*10^380 x^692 - 1.685107150526525*10^373 x^694 +
   4.210534545492902*10^365 x^696 - 1.013105481444205*10^358 x^698 +
   2.346299337286123*10^350 x^700 - 5.227813821621668*10^342 x^702 +
   1.120092727822506*10^335 x^704 - 2.306568812170204*10^327 x^706 +
   4.562790569051598*10^319 x^708 - 8.665839615324031*10^311 x^710 +
   1.57929*10^304 x^712 - 2.76013*10^296 x^714 +
   4.62324*10^288 x^716 - 7.41716*10^280 x^718 +
   1.13897*10^273 x^720 - 1.67291*10^265 x^722 +
   2.34855*10^257 x^724 - 3.14893*10^249 x^726 +
   4.0292*10^241 x^728 - 4.9159*10^233 x^730 + 5.71392*10^225 x^732 -
   6.32137*10^217 x^734 + 6.64985*10^209 x^736 -
   6.64492*10^201 x^738 + 6.30048*10^193 x^740 -
   5.66194*10^185 x^742 + 4.81655*10^177 x^744 -
   3.87369*10^169 x^746 + 2.94125*10^161 x^748 -
   2.10534*10^153 x^750 + 1.41845*10^145 x^752 - 8.98*10^136 x^754 +
   5.33242*10^128 x^756 - 2.96423*10^120 x^758 +
   1.53931*10^112 x^760 - 7.45037*10^103 x^762 +
   3.35264*10^95 x^764 - 1.39887*10^87 x^766 + 5.39579*10^78 x^768 -
   1.91778*10^70 x^770 + 6.25793*10^61 x^772 - 1.86721*10^53 x^774 +
   5.07121*10^44 x^776 - 1.24727*10^36 x^778 + 2.76185*10^27 x^780 -
   5.46899*10^18 x^782 + 9.60895*10^9 x^784 - 14.8419 x^786 +
   1.9931*10^-8 x^788 - 2.29559*10^-17 x^790 + 2.22936*10^-26 x^792 -
   1.78565*10^-35 x^794 + 1.14492*10^-44 x^796 -
   5.63037*10^-54 x^798 + 1.98626*10^-63 x^800 -
   4.45525*10^-73 x^802 + 4.74795*10^-83 x^804;

Plot[P, {x, 0, 100},PlotRange->All]

P[x_]:= Your large expression here

ListLogPlot[Table[{x, P[x]}, {x, 0, 100, 10}], PlotRange -> All, Frame -> True]

NSolve[P[x] == 0, x]