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 A109976 #18 May 28 2018 03:41:28
%S A109976 1,2,3,6,7,16,19,46,66,159,274,667,1320,3263,7156,18084,42794,111018,
%T A109976 278752,743889,1959482,5383395,14761634,41740307,118517301,344580865,
%U A109976 1009349749,3013665637,9081346743,27808754039,86015003997,269796018547
%N A109976 Diagonal sums of number triangle A109974.
%H A109976 Robert Israel, <a href="/A109976/b109976.txt">Table of n, a(n) for n = 0..1063</a>
%F A109976 a(n) = Sum_{k=0..floor(n/2)} sigma_k(n-2k+1). - Corrected by _Robert Israel_, May 25 2018
%F A109976 G.f.: Sum_{n>=1} x^(n-1)/((1-x^n)*(1-n*x^2)). - _Robert Israel_, May 27 2018
%p A109976 f:= n -> add(numtheory:-sigma[k](n-2*k+1),k=0..n/2):
%p A109976 map(f, [$0..50]); # _Robert Israel_, May 25 2018
%t A109976 Array[Sum[DivisorSigma[k, (# - 2 k + 1)], {k, 0, Floor[#/2]}] &, 32, 0] (* _Michael De Vlieger_, May 27 2018 *)
%Y A109976 Cf. A109974
%K A109976 easy,nonn
%O A109976 0,2
%A A109976 _Paul Barry_, Jul 06 2005