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 A064592 #18 Jan 05 2025 19:51:36 %S A064592 2520,31320,1163160,2208384,3053232,6535296,13472928,123165600, %T A064592 365959296,4401782352,5517818880,612014161920 %N A064592 Nonunitary doubly perfect numbers: the sum of the nonunitary divisors of n is 2n; i.e., sigma(n) - usigma(n) = 2n. %C A064592 There are no others up to 7.9*10^12, but here's a larger one: 2846972800010800140288. %C A064592 Ligh & Wall found the first 11 terms of this sequence. - _Amiram Eldar_, Sep 27 2018 %H A064592 Steve Ligh and Charles R. Wall, <a href="https://web.archive.org/web/2024*/https://www.fq.math.ca/Scanned/25-4/ligh.pdf">Functions of Nonunitary Divisors</a>, Fibonacci Quarterly, Vol. 25 (1987), pp. 333-338. %t A064592 nusigma[ n_ ] := DivisorSigma[ 1, n ]-Times@@(1+Power@@#&/@FactorInteger[ n ]); For[ n=1, True, n++, If[ nusigma[ n ]==2n, Print[ n ] ] ] %o A064592 (PARI) isok(n) = sumdiv(n, d, if (gcd(d, n/d)!=1, d)) == 2*n; \\ _Michel Marcus_, Jul 31 2017 %Y A064592 Cf. A048146, A064591, A064593, A064594, A064595, A064596. %K A064592 nonn,hard %O A064592 1,1 %A A064592 _Dean Hickerson_, Sep 25 2001