OFFSET
1,1
LINKS
Jon E. Schoenfield, Table of n, a(n) for n = 1..10000 (first 1000 terms from Vincenzo Librandi)
EXAMPLE
4 is not a term: its proper divisors are 1 and 2, and their average is (1+2)/2 = 3/2.
6 is a term: its proper divisors are 1, 2, and 3, and their average is (1+2+3)/3 = 6/3 = 2.
MATHEMATICA
Select[Range[400], !PrimeQ[#]&&IntegerQ[Mean[Most[ Divisors[ #]]]]&] (* Harvey P. Dale, Jun 28 2011 *)
PROG
(PARI) isok(n) = (n != 1) && !isprime(n) && !((sigma(n) - n) % (numdiv(n)-1)); \\ Michel Marcus, Mar 28 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved