Atomic Number chemistry counter thing

-- In chemistry class, we were forced to count the number of electrons in certain atoms using a weird old scientist man techinque, so I decided to
-- write a script to force the computer to do it for me instead.  Is that too evil? I think not.

local tab = {"1s","2s","2p","3s","3p","4s","3d","4p","5s","4d","5p","6s","4f","5d","6p","7s","5f","6d","7p","6f","7d","7f"}
electrons = 71 -- 156 is the largest number you can calculate

function define(x)
    local k = string.sub(x,2,2)
    if k == "s" then
        return 2
    elseif k == "p" then
         return 6
    elseif k == "d" then
        return 10
    elseif k == "f" then
        return 14
    end
end

function tosuperscript(x)
    local sup = {"⁰","¹","²","³","⁴","⁵","⁶","⁷","⁸","⁹","¹⁰","¹¹","¹²","¹³","¹⁴","¹⁵","¹⁶","¹⁷","¹⁸","¹⁹"}
    return sup[x+1]
end
local out = ""
for i=1,#tab do
    local k = define(tab[i])
    local sum = electrons - k
    if sum > 0 then
        electrons = electrons - k
        out = out..tab[i]..tosuperscript(k).." "
    else
        local newsum = electrons -- problems may orginate from here
        out = out..tab[i]..tosuperscript(newsum).." "
        break
    end
end

print(out)