A023884 - OEIS

%I #26 Feb 20 2023 19:52:35

%S 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,

%T 59,61,67,69,71,73,79,81,83,87,89,91,97,101,103,107,109,113,114,117,

%U 120,121,123,124,127,131,133,135,137,139,141,149,151,157,159

%N Average of divisors except itself is an integer.

%C All the prime numbers (A000040) are in this sequence. But there are other numbers (A023885). - _Daniel Lignon_, Feb 26 2015

%H Daniel Lignon, <a href="/A023884/b023884.txt">Table of n, a(n) for n = 1..1000</a>

%p q:=n->(irem(numtheory[sigma](n)-n,numtheory[tau](n)-1)=0):

%p select(q,[$2..159])[]; # _Lorenzo Sauras Altuzarra_, Feb 01 2023

%t Select[Range[2000],IntegerQ[Mean[Most[Divisors[#]]]]&] (* _Daniel Lignon_, Feb 26 2015 *)

%o (PARI) isok(n) = (n != 1) && !((sigma(n) - n) % (numdiv(n)-1)); \\ _Michel Marcus_, Mar 01 2015

%Y Cf. A000040, A023885.

%K nonn

%O 1,1

%A _Olivier Gérard_