答えは約 0.000127 (1/7900)
になったけど合ってるかな?
fact = lambda n: n and n * fact(n - 1) or 1
combi = lambda n,m: fact(n) / fact(m) / fact(n-m)
a = combi(13,13) * pow(6,13) + \
combi(13,11) * pow(6,11) * combi( 2, 1) + \
combi(13, 9) * pow(6, 9) * combi( 4, 2) + \
combi(13, 7) * pow(6, 7) * combi( 6, 3) + \
combi(13, 5) * pow(6, 5) * combi( 8, 4) + \
combi(13, 3) * pow(6, 3) * combi(10, 5) + \
combi(13, 1) * pow(6, 1) * combi(12, 6)
b = combi(53,26)
print float(a) / float(b)