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 A094590 #8 Apr 09 2014 10:15:00
%S A094590 1,1,2,6,18,54,216,864,3456,13824,55296,221184,884736,3538944,
%T A094590 14155776,56623104,226492416,905969664,4529848320,22649241600,
%U A094590 113246208000,566231040000,2831155200000,14155776000000,70778880000000
%N A094590 a(1) = 1; a(n+1) = a(n) * k(n), where k(n) is the number of elements of {a(j)}, 1<=j<=n, which are <= n.
%Y A094590 Cf. A094589.
%K A094590 nonn,easy
%O A094590 1,3
%A A094590 _Leroy Quet_, Jun 07 2004
%E A094590 More terms from _Vladeta Jovovic_, Jun 13 2004