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 A220290 #28 Jun 02 2025 05:02:07 %S A220290 1950625,1220640625,186264514898681640625 %N A220290 4-hyperperfect numbers: n = 4*(sigma(n)-n-1) + 1. %C A220290 For all k in A059613, (5^k-4)*5^(k-1) is a term. In particular, k=15 gives a term 186264514898681640625. %H A220290 Judson S. McCranie, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL3/mccranie.html">A Study of Hyperperfect Numbers</a>, Journal of Integer Sequences, Vol. 3 (2000), Article 00.1.3. %H A220290 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/HyperperfectNumber.html">Hyperperfect Number</a> %t A220290 Select[Range[1, 2*10^6, 4], # + 3 == 4*(DivisorSigma[1, #] - #) &] %Y A220290 Cf. A000396, A007593, A028499-A028502, A034916. %K A220290 bref,hard,more,nonn %O A220290 1,1 %A A220290 _Arkadiusz Wesolowski_, Dec 11 2012 %E A220290 a(3) from _Max Alekseyev_, Jun 01 2025