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 A321259 #17 Feb 16 2025 08:33:57
%S A321259 0,1,1,17,1,794,1,65793,19684,9766650,1,2194095090,1,678223089234,
%T A321259 30531927033,281479271743489,1,150196195641350171,1,
%U A321259 100000096466944316978,558545874543637211,81402749386839765307626,1,79501574308536809523296482,298023223876953126
%N A321259 a(n) = sigma_n(n) - n^n.
%C A321259 a(n) is the sum of n-th powers of proper divisors of n.
%H A321259 Seiichi Manyama, <a href="/A321259/b321259.txt">Table of n, a(n) for n = 1..400</a>
%H A321259 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ProperDivisor.html">Proper divisors</a>
%H A321259 <a href="/index/Su#sums_of_divisors">Index entries for sequences related to sums of divisors</a>
%F A321259 G.f.: Sum_{k>=1} (k*x)^(2*k)/(1 - (k*x)^k).
%F A321259 a(n) = A023887(n) - A000312(n).
%F A321259 a(n) = A321258(n,n).
%F A321259 a(n) = 1 if n is prime.
%t A321259 Table[DivisorSigma[n, n] - n^n, {n, 25}]
%t A321259 nmax = 25; Rest[CoefficientList[Series[Sum[(k x)^(2 k)/(1 - (k x)^k), {k, 1, nmax}], {x, 0, nmax}], x]]
%o A321259 (Magma) [DivisorSigma(n, n) - n^n: n in [1..30]]; // _Vincenzo Librandi_, Nov 02 2018
%o A321259 (PARI) a(n) = sigma(n, n) - n^n; \\ _Michel Marcus_, Nov 02 2018
%Y A321259 Cf. A000312, A001065, A023887, A067558, A276634, A279363, A279364, A292919, A321258.
%K A321259 nonn
%O A321259 1,4
%A A321259 _Ilya Gutkovskiy_, Nov 01 2018