Possible=()
Last_Impossible=1
Successive_Possible=0
n=1
maxc=n/20
maxb=n/9
maxa=n/6

while Successive_Possible < 6:
    for c in range(0,3):
        for b in range(0,5):
            for a in range(0,7):
                if (6*a)+(9*b)+(20*c)==n:
                    Possible +=(n,)
                    break
            if n in Possible:
                break
        if n in Possible:
            break
    #Put counter conditional here, and then your else clause after it
    if n in Possible:
        #Counter stuff
        Successive_Possible +=1
        print "Successive Possible #:",Successive_Possible,"Number:",n
        n+=1
    else:
        #What do you think?
        Last_Impossible=n
        Successive_Possible=0
        n+=1

print Possible
print Last_Impossible