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A283970
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Integers m such that m divides sigma_2(m) - k where k is some divisor of m.
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1
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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
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OFFSET
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1,2
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LINKS
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EXAMPLE
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2 is in this sequence because 2 divides A001157(2) - 1 = 5 - 1 = 4.
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MATHEMATICA
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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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PROG
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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]];
(PARI) isok(n) = fordiv(n, d, if (!((sigma(n, 2) - d) % n), return (1))); \\ Michel Marcus, Mar 18 2017
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CROSSREFS
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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.
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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