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 A156296 #20 Apr 02 2017 10:36:56
%S A156296 1,2,10,140,5740,700280,255602200,279628806800,917462115110800,
%T A156296 9029662136920493600,266600774592577573540000,
%U A156296 23613897008762965998731960000,6274708327065504088149055143160000
%N A156296 a(1)=1, a(n) = 2 * Sum_{k=1..n-1} (3^k-1)/2 * a(k) for n>=2.
%H A156296 Michael De Vlieger, <a href="/A156296/b156296.txt">Table of n, a(n) for n = 0..64</a>
%F A156296 a(n) = 2*A015502(n+1) for n>1. - _Joe Slater_, Mar 23 2017
%t A156296 Table[QPochhammer[-1, 3, n+1]/2^(n+1), {n, 0, 15}] (* _Vaclav Kotesovec_, Mar 24 2017 *)
%K A156296 nonn,easy
%O A156296 0,2
%A A156296 _Roger L. Bagula_, Feb 07 2009
%E A156296 New name from _Joerg Arndt_, Mar 24 2017