This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A279886 #7 Dec 22 2016 23:37:00
%S A279886 1,4,66,7200,6917400,72442188000,9822893856930000,
%T A279886 19942863749656848000000,687732249521129504041350000000,
%U A279886 450437284567157389148103391935000000000,6194243041031315772374678081343893262937500000000
%N A279886 a(n) = A057863(n+1) * Sum_{k=0..n}(k! / (2*k+1)!!).
%H A279886 Daniel Suteu, <a href="/A279886/b279886.txt">Table of n, a(n) for n = 0..29</a>
%F A279886 a(n) ~ Pi/2 * A057863(n+1).
%F A279886 a(0) = 1, a(n) = a(n-1) * (2*n+1)!! + n! * A057863(n).
%t A279886 Table[Product[(2 k - 1)!!, {k, n + 1}] Sum[(j!/(2 j + 1)!!), {j, 0, n}], {n, 0, 10}] (* _Michael De Vlieger_, Dec 22 2016 *)
%o A279886 (PARI) a(n) = prod(k=0,n,prod(i=0, k, 2*i+1))*sum(k=0,n,k!/prod(i=0,k,2*i+1));
%Y A279886 Cf. A057863.
%K A279886 nonn,easy
%O A279886 0,2
%A A279886 _Daniel Suteu_, Dec 21 2016