http://rio2016.2ch.net/test/read.cgi/math/1493648300/331
>331 ：１３２人目の素数さん ：2017/05/14(日) 14:00:19.11 ID:aOBm0ly2
>>>237
>
>sum binomial(15, i)*4^(15-i) from i = 5 to 15 = 5012015501
>5 * 5012015501 = 25060077505
>
>sum binomial(15, i)*binomial(15-i, j)*3^(15-i-j) from j = 5 to 15-i from i = 5 to 10 = 323173994
>binomial(5, 2) * 323173994 = 3231739940
>
>binomial(15, 5) * binomial(10, 5) = 756756
>
>25060077505 - 3231739940 + 756756 = 21829094321
>
>5^15 = 30517578125
>
>21829094321 / 30517578125 = 0.715295762710528