cp's OEIS Frontend

A283970 Integers m such that m divides sigma_2(m) - k where k is some divisor of m.

%I A283970 #36 Nov 21 2024 21:25:46
%S A283970 1,2,3,4,5,6,7,9,10,11,12,13,15,17,19,23,25,29,30,31,35,36,37,40,41,
%T A283970 43,47,48,49,50,53,59,60,61,65,67,71,73,76,79,83,89,97,101,103,107,
%U A283970 109,113,120,121,127,130,131,132,136,137,139,140,149,150,151,157,163,167,169,173,175,179,180
%N A283970 Integers m such that m divides sigma_2(m) - k where k is some divisor of m.
%e A283970 2 is in this sequence because 2 divides A001157(2) - 1 = 5 - 1 = 4.
%t A283970 Select[Range@ 180, Function[n, Total@ Boole@ Map[Divisible[ DivisorSigma[2, n] - #, n] &, Divisors@ n] > 0]] (* _Michael De Vlieger_, Mar 19 2017 *)
%o A283970 (Magma) [[n: k in [1..n] | Denominator(n/k) eq 1 and
%o A283970 Denominator(((DivisorSigma(2, n))-k)/n) eq 1]: n in [1..100]];
%o A283970 (PARI) isok(n) = fordiv(n, d, if (!((sigma(n, 2) - d) % n), return (1))); \\ _Michel Marcus_, Mar 18 2017
%Y A283970 Supersequence of A166684.
%Y A283970 Cf. A001157 (sigma_2(n): sum of squares of divisors of n), A205523 (integers n such that n divides sigma_1(n) - i where i is some divisor of n), A284082.
%K A283970 nonn
%O A283970 1,2
%A A283970 _Juri-Stepan Gerasimov_, Mar 18 2017