A069168 Numbers k such that sigma(k) * Sum_{d|k} (1/sigma(d)) is not an integer.

4, 8, 9, 12, 16, 20, 24, 25, 27, 32, 36, 44, 45, 48, 49, 50, 54, 56, 60, 63, 64, 68, 72, 75, 80, 81, 88, 92, 96, 98, 99, 100, 104, 108, 112, 116, 117, 121, 125, 128, 132, 135, 136, 144, 147, 150, 153, 160, 162, 164, 168, 169, 171, 175, 176, 180, 184, 188, 189, 192

Offset

1,1

Comments

A proper subset of A013929. - Robert G. Wilson v, Jul 21 2012

Links

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

Mathematica

fQ[n_] := !IntegerQ[ DivisorSigma[1, n] Plus @@ (1/DivisorSigma[1, Divisors[n]])]; Select[ Range@ 200, fQ] (* Robert G. Wilson v, Jul 21 2012 *)

Prog

(PARI) isok(k) = denominator(sigma(k)*sumdiv(k, d, 1/sigma(d))) != 1; \\ Michel Marcus, Feb 09 2021

Crossrefs

Cf. A000203, A013929.

Sequence in context: A375399 A371601 A283050 * A374037 A102211 A244032

Adjacent sequences: A069165 A069166 A069167 * A069169 A069170 A069171

Keyword

easy,nonn

Author

Benoit Cloitre, Apr 09 2002

Status

approved