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 A053223 #23 Oct 27 2023 22:00:45
%S A053223 -1,2,-4,7,-10,11,-9,7,-11,22,-30,24,-10,7,-20,34,-40,41,-32,14,-16,
%T A053223 48,-65,40,-13,18,-42,68,-82,71,-46,21,-12,49,-96,75,-26,38,-82,102,
%U A053223 -106,92,-46,0,-18,100,-143,103,-57,47,-70,110,-114,96,-88,50,-40,138,-214,140,-26,15,-66
%N A053223 Second differences of sigma(n).
%H A053223 T. D. Noe, <a href="/A053223/b053223.txt">Table of n, a(n) for n = 1..10000</a>
%F A053223 G.f.: -1 - 1/x + (1 - x)^2*Sum_{k>=1} k*x^(k-2)/(1 - x^k). - _Ilya Gutkovskiy_, Jan 29 2017
%t A053223 Table[DivisorSigma[1,n+2] - 2*DivisorSigma[1,n+1] + DivisorSigma[1,n], {n,1,100}] (* _G. C. Greubel_, Sep 03 2018 *)
%o A053223 (PARI) a(n)=sigma(n+2)-2*sigma(n+1)+sigma(n) \\ _Charles R Greathouse IV_, Mar 09 2014
%o A053223 (Magma) [DivisorSigma(1, n+2) - 2*DivisorSigma(1,n+1) + DivisorSigma(1, n): n in [1..100]]; // _G. C. Greubel_, Sep 03 2018
%Y A053223 Cf. A000203, A053222, A053228, A053229, A053247, A053248.
%Y A053223 Indices of 0: A099632 - 1.
%K A053223 sign
%O A053223 1,2
%A A053223 _Asher Auel_, Jan 06 2000