A069169 Nonprimes k such that sigma(k)*Sum_{d|k} 1/sigma(d) is an integer.

1, 6, 10, 14, 15, 18, 21, 22, 26, 28, 30, 33, 34, 35, 38, 39, 40, 42, 46, 51, 52, 55, 57, 58, 62, 65, 66, 69, 70, 74, 76, 77, 78, 82, 84, 85, 86, 87, 90, 91, 93, 94, 95, 102, 105, 106, 110, 111, 114, 115, 118, 119, 120, 122, 123, 124, 126, 129, 130, 133, 134, 138, 140

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Mathematica

q[n_] := IntegerQ[DivisorSigma[1, n]*DivisorSum[n, 1/DivisorSigma[1, #] &]]; Select[Range[140], !PrimeQ[#] && q[#] &] (* Amiram Eldar, Apr 30 2022 *)

Prog

(PARI) isok(k) = !isprime(k) && (denominator(sigma(k)*sumdiv(k, d, 1/sigma(d))) == 1); \\ Michel Marcus, Apr 30 2022

Crossrefs

Cf. A000203, A265709, A265710.

Sequence in context: A132982 A354922 A300080 * A230766 A231877 A080364

Adjacent sequences: A069166 A069167 A069168 * A069170 A069171 A069172

Keyword

easy,nonn

Author

Benoit Cloitre, Apr 09 2002

Status

approved