A072910 a(n) = sigma(A023883(n)) / tau(A023883(n)).

1, 3, 6, 6, 7, 8, 9, 10, 9, 12, 12, 15, 14, 12, 14, 13, 18, 19, 18, 15, 18, 15, 20, 14, 24, 21, 18, 21, 24, 18, 24, 21, 27, 33, 30, 28, 28, 32, 36, 30, 21, 26, 27, 24, 27, 38, 30, 36, 35, 45, 36, 42, 39, 26, 44, 28, 40, 51, 30, 36, 28, 48, 54, 42, 45, 38, 31, 39, 36, 48, 60, 54

Offset: 1

Author

Benoit Cloitre, Aug 10 2002

Keywords

• easy
• nonn

Comments

Arithmetic means of divisors of nonprime arithmetic numbers (A023883). - Amiram Eldar, Jun 06 2020

Links

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

Crossrefs

Cf. A000005, A000203, A003601, A102187, A023883.

Programs

Mathematica

meanDiv[n_] := DivisorSigma[1, n]/DivisorSigma[0, n]; Select[meanDiv /@ Select[Range[200], !PrimeQ[#] &], IntegerQ] (* Amiram Eldar, Jun 06 2020 *)

PARI

f(x) = sigma(x)/numdiv(x);
apply(x->f(x), select(x->((denominator(f(x))==1) && !isprime(x)), [1..1000])) \\ Michel Marcus, Jun 06 2020