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 A111308 #7 Apr 09 2014 10:16:39
%S A111308 0,1,4,10,28,71,204,556,1716,5049,16884,53418,193500,654639,2560140,
%T A111308 9209016,38697300,147193425,661035060,2645445870,12627252540,
%U A111308 52926443415,267088884300,1167777120420,6200158778100,28178714373705
%N A111308 Sum_{k=1..n} k!! * (n+1-k)!!, where k!! = k*(k-2)*(k-4)..*(1 or 2).
%e A111308 a(5) = 1 *5*3*1 + 2 *4*2 + 3*1 *3*1 + 4*2 *2 + 5*3*1 *1 = 15 + 16 + 9 + 16 + 15 = 71.
%t A111308 Table[ Sum[k!!(n + 1 - k)!!, {k, n}], {n, 25}] (* _Robert G. Wilson v_ *)
%Y A111308 Cf. A006882.
%K A111308 easy,nonn
%O A111308 0,3
%A A111308 _Leroy Quet_, Nov 03 2005
%E A111308 More terms from _Robert G. Wilson v_, Nov 04 2005