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 A181893 #15 Apr 16 2012 12:54:57
%S A181893 1,1,1,3,7,16,34,70,130,235,445,769,1417,2497,4177,6529,11233,17713,
%T A181893 30673,49033,76233,119433,205833,316713,471945,715881,1026345,1449705,
%U A181893 2296425,3376425,5536425,8128425,11814825,17528745,25242537,34480425,52956201,81509673
%N A181893 Number of different nonnegative solutions of equation: x^2 - y^2 = k! for 1 <= k <= n.
%F A181893 a(n)=sum(k=1..n, A138196(k) )
%t A181893 kkk = 1; cc = {1, 1, 1}; Do[w = n!/4; kk = Floor[(DivisorSigma[0, w] + 1)/2]; kkk = kkk + kk; AppendTo[cc, kkk], {n, 4, 54}]; cc
%Y A181893 Cf. A138196, A139151, A181892.
%K A181893 nonn
%O A181893 1,4
%A A181893 _Artur Jasinski_, Mar 31 2012