A023884 Average of divisors except itself is an integer.

2, 3, 5, 6, 7, 9, 11, 13, 15, 17, 19, 23, 25, 29, 30, 31, 33, 37, 41, 43, 44, 47, 49, 51, 53, 59, 61, 67, 69, 71, 73, 79, 81, 83, 87, 89, 91, 97, 101, 103, 107, 109, 113, 114, 117, 120, 121, 123, 124, 127, 131, 133, 135, 137, 139, 141, 149, 151, 157, 159

Offset

1,1

Comments

All the prime numbers (A000040) are in this sequence. But there are other numbers (A023885). - Daniel Lignon, Feb 26 2015

Links

Daniel Lignon, Table of n, a(n) for n = 1..1000

Maple

q:=n->(irem(numtheory[sigma](n)-n, numtheory[tau](n)-1)=0):
select(q, [$2..159])[]; # Lorenzo Sauras Altuzarra, Feb 01 2023

Mathematica

Select[Range[2000], IntegerQ[Mean[Most[Divisors[#]]]]&] (* Daniel Lignon, Feb 26 2015 *)

Prog

(PARI) isok(n) = (n != 1) && !((sigma(n) - n) % (numdiv(n)-1)); \\ Michel Marcus, Mar 01 2015

Crossrefs

Cf. A000040, A023885.

Sequence in context: A057165 A245395 A347498 * A135607 A376471 A358221

Adjacent sequences: A023881 A023882 A023883 * A023885 A023886 A023887

Keyword

nonn

Author

Olivier Gérard

Status

approved