A283970 Integers m such that m divides sigma_2(m) - k where k is some divisor of m.
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, 43, 47, 48, 49, 50, 53, 59, 60, 61, 65, 67, 71, 73, 76, 79, 83, 89, 97, 101, 103, 107, 109, 113, 120, 121, 127, 130, 131, 132, 136, 137, 139, 140, 149, 150, 151, 157, 163, 167, 169, 173, 175, 179, 180
Offset: 1
Keywords
Examples
2 is in this sequence because 2 divides A001157(2) - 1 = 5 - 1 = 4.
Crossrefs
Programs
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Magma
[[n: k in [1..n] | Denominator(n/k) eq 1 and Denominator(((DivisorSigma(2, n))-k)/n) eq 1]: n in [1..100]];
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Mathematica
Select[Range@ 180, Function[n, Total@ Boole@ Map[Divisible[ DivisorSigma[2, n] - #, n] &, Divisors@ n] > 0]] (* Michael De Vlieger, Mar 19 2017 *)
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PARI
isok(n) = fordiv(n, d, if (!((sigma(n, 2) - d) % n), return (1))); \\ Michel Marcus, Mar 18 2017