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 A245774 #27 Sep 08 2022 08:46:09 %S A245774 1,3,6,12,28,84,120,234,270,496,672,1080,1488,1638,6048,6552,8128, %T A245774 24384,30240,32760,35640,199584,435708,523776,2142720,2178540,4713984, %U A245774 12999168,18506880,23569920,33550336,36197280,45532800 %N A245774 Numbers k that divide 3*sigma(k). %C A245774 Numbers k that divide 3*A000203(k). %C A245774 Supersequence of A007691 and A245775. %C A245774 Union of A007691 and 3*A227303. - _Robert Israel_, Aug 26 2014 %e A245774 Number 12 is in the sequence because 12 divides 3*sigma(12) = 3*28. %p A245774 select(n -> 3*numtheory:-sigma(n) mod n = 0, [$1..10^6]); # _Robert Israel_, Aug 26 2014 %t A245774 a245774[n_Integer] := Select[Range[n], Divisible[3*DivisorSigma[1, #], #] == True &]; a245774[10^7] (* _Michael De Vlieger_, Aug 27 2014 *) %o A245774 (Magma) [n: n in [1..3000000] | Denominator(3*(SumOfDivisors(n))/n) eq 1] %o A245774 (PARI) %o A245774 for(n=1,10^9,if((3*sigma(n))%n==0,print1(n,", "))) \\ _Derek Orr_, Aug 26 2014 %Y A245774 Cf. A000203 (sum of divisors), A007691 (multiply-perfect numbers). %Y A245774 Cf. A227303 (n divides sigma(3n)), A245775 (denominator(sigma(n)/n) = 3). %Y A245774 Cf. A272027 (3*sigma(n)). %K A245774 nonn %O A245774 1,2 %A A245774 _Jaroslav Krizek_, Aug 26 2014