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 A277374 #17 May 17 2018 09:14:46
%S A277374 1,2,3,6,50,100,1794,3588,114840,229680,11483880,22967760,1653679440,
%T A277374 3307358880,324121165200,648242330400,82975018331520,165950036663040,
%U A277374 26883905939049600,53767811878099200,10753562375623468800,21507124751246937600,5204724189801718982400
%N A277374 a(n) = 2^n*floor(n/2)!*Gamma(ceiling((n+1)/2),-1/4)*exp(-1/4).
%H A277374 G. C. Greubel, <a href="/A277374/b277374.txt">Table of n, a(n) for n = 0..445</a>
%F A277374 a(n) ~ Pi*exp(-1/4-n)*n^(n+1) if n is even, a(n) ~ 2*Pi*exp(3/4-n)*(n-1)^n if n is odd. - _Vladimir Reshetnikov_, Oct 19 2016
%p A277374 a := n -> 2^n*floor(n/2)!*GAMMA(ceil((n+1)/2),-1/4)*exp(-1/4):
%p A277374 seq(simplify(a(n)),n=0..22);
%t A277374 a[n_] := 2^n Floor[n/2]! Gamma[Ceiling[(1 + n)/2],-1/4] Exp[-1/4];
%t A277374 FunctionExpand@Table[a[n], {n,0,22}]
%o A277374 (PARI) for(n=0, 20, print1(round(2^n*(floor(n/2))!*exp(-1/4)* incgam(ceil((n +1)/2), -1/4)), ", ")) \\ _G. C. Greubel_, May 16 2018
%Y A277374 a(n) * A056040(n) = A277393(n).
%K A277374 nonn
%O A277374 0,2
%A A277374 _Peter Luschny_, Oct 17 2016