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 A246454 #24 Nov 25 2024 12:15:24 %S A246454 1,2,6,24,28,120,496,672,4320,4680,8128,26208,30240,32760,523776, %T A246454 2178540,8910720,17428320,20427264,23569920,33550336,45532800, %U A246454 91963648,142990848,197064960,459818240,1379454720,1476304896,8583644160,8589869056,10200236032 %N A246454 Numbers k that divide 2*sigma(k). %C A246454 Numbers k such that 2*A000203(k) / k is an integer. %C A246454 Union of A007691 (multiply-perfect numbers) and A159907 (numbers with half-integral abundancy index). %H A246454 Jens Kruse Andersen, <a href="/A246454/b246454.txt">Table of n, a(n) for n = 1..55</a> %e A246454 Number 24 is in the sequence because 24 divides 2*sigma(24); 24 divides 2*60. %o A246454 (Magma) [n: n in [1..1000000] | Denominator(2*(SumOfDivisors(n))/n) eq 1]; %o A246454 (PARI) %o A246454 for(n=1,10^8,if((2*sigma(n))%n==0,print1(n,", "))) \\ _Derek Orr_, Aug 26 2014 %Y A246454 Cf. A000203, A007691, A159907. %K A246454 nonn %O A246454 1,2 %A A246454 _Jaroslav Krizek_, Aug 26 2014