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 A363630 #21 Jan 04 2025 06:15:11
%S A363630 -3,3,-13,18,-24,21,-39,63,-68,48,-81,127,-108,87,-170,216,-174,156,
%T A363630 -213,294,-302,201,-303,497,-375,276,-474,537,-468,426,-531,777,-686,
%U A363630 462,-726,965,-744,573,-938,1200,-906,798,-993,1251,-1306,831,-1179,1875,-1314,1023,-1562,1722,-1488,1290,-1698
%N A363630 Expansion of Sum_{k>0} (1/(1+x^k)^3 - 1).
%H A363630 Seiichi Manyama, <a href="/A363630/b363630.txt">Table of n, a(n) for n = 1..10000</a>
%F A363630 G.f.: Sum_{k>0} binomial(k+2,2) * (-x)^k/(1 - x^k).
%F A363630 a(n) = Sum_{d|n} (-1)^d * binomial(d+2,2).
%F A363630 a(n) = -(A321543(n) + 3*A002129(n) + 2*A048272(n)) / 2. - _Amiram Eldar_, Jan 04 2025
%t A363630 a[n_] := DivisorSum[n, (-1)^#*Binomial[# + 2, 2] &]; Array[a, 50] (* _Amiram Eldar_, Jul 18 2023 *)
%o A363630 (PARI) a(n) = sumdiv(n, d, (-1)^d*binomial(d+2, 2));
%Y A363630 Cf. A002129, A048272, A321543, A363629, A363631.
%Y A363630 Cf. A320900, A363022, A363615.
%K A363630 sign,easy
%O A363630 1,1
%A A363630 _Seiichi Manyama_, Jun 12 2023