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 A372625 #5 May 08 2024 08:52:48
%S A372625 1,-1,1,3,1,-5,1,3,10,-5,1,-6,1,-5,10,19,1,-14,1,-13,10,-5,1,10,26,-5,
%T A372625 10,-13,1,-39,1,19,10,-5,26,14,1,-5,10,-6,1,-50,1,-13,35,-5,1,46,50,
%U A372625 -30,10,-13,1,-50,26,-30,10,-5,1,-11,1,-5,59,83,26,-50,1,-13,10,-79
%N A372625 Expansion of Sum_{k>=1} k^2 * x^(k^2) / (1 + x^k).
%F A372625 a(n) = Sum_{d|n, d <= sqrt(n)} (-1)^(d + n/d) * d^2.
%t A372625 nmax = 70; CoefficientList[Series[Sum[k^2 x^(k^2)/(1 + x^k), {k, 1, nmax}], {x, 0, nmax}], x] // Rest
%t A372625 Table[DivisorSum[n, (-1)^(# + n/#) #^2 &, # <= Sqrt[n] &], {n, 1, 70}]
%Y A372625 Cf. A064027, A066839, A078306, A095118, A321543, A321558, A348608.
%K A372625 sign
%O A372625 1,4
%A A372625 _Ilya Gutkovskiy_, May 07 2024