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 A139486 #10 Jan 03 2021 23:21:12
%S A139486 1,3,12,72,720,12960,440640,29082240,3780691200,975418329600,
%T A139486 501365021414400,514400511971174400,1054521049540907520000,
%U A139486 4321427261018639016960000,35409774976786728104970240000,580224572769627326728042352640000
%N A139486 a(n) = Product_{j=0..n-1} (2^j + 2).
%F A139486 a(n) = A139485(2^n + 1) - 1 = Sum_{j=1..2^n} A139485(j).
%F A139486 For n >= 1, a(n) = 2^(n-1) * 3 * A028361(n-1).
%o A139486 (PARI) { a(n) = prod(j=0,n-1,2^j+2) }
%Y A139486 Cf. A139485, A028361.
%K A139486 easy,nonn
%O A139486 0,2
%A A139486 _Leroy Quet_, Apr 23 2008
%E A139486 Edited and extended by _Max Alekseyev_, Oct 24 2008