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 A067558 #23 Dec 31 2024 06:32:07
%S A067558 0,1,1,5,1,14,1,21,10,30,1,66,1,54,35,85,1,131,1,146,59,126,1,274,26,
%T A067558 174,91,266,1,400,1,341,131,294,75,615,1,366,179,610,1,736,1,626,341,
%U A067558 534,1,1106,50,755,299,866,1,1184,147,1114,371,846,1,1860,1,966,581,1365
%N A067558 Sum of squares of proper divisors of n.
%H A067558 T. D. Noe, <a href="/A067558/b067558.txt">Table of n, a(n) for n=1..10000</a>
%F A067558 a(n) = A001157(n) - n^2.
%F A067558 a(n) = 1 if and only if n is prime.
%F A067558 Dirichlet g.f.: zeta(s-2)*(zeta(s) - 1). - _Ilya Gutkovskiy_, Sep 08 2016
%F A067558 Sum_{k=1..n} a(k) ~ (zeta(3)-1) * n^3 / 3. - _Amiram Eldar_, Dec 31 2024
%e A067558 a(12) = 1^2 + 2^2 + 3^2 + 4^2 + 6^2 = 1 + 4 + 9 + 16 + 36 = 66.
%t A067558 Table[DivisorSigma[2, n] - n^2, {n, 1, 64}] (* _Jean-François Alcover_, Mar 01 2019 *)
%o A067558 (PARI) a(n)=sigma(n,2)-n^2 \\ _Charles R Greathouse IV_, Dec 07 2011
%Y A067558 Cf. A001157, A002117, A032741.
%K A067558 nonn,easy
%O A067558 1,4
%A A067558 _Reinhard Zumkeller_, Jan 29 2002