A158298 Denominators of averages of squares of the divisors of n.

1, 2, 1, 1, 1, 2, 1, 4, 3, 2, 1, 1, 1, 2, 1, 5, 1, 6, 1, 1, 1, 2, 1, 4, 1, 2, 1, 1, 1, 2, 1, 2, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 1, 3, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 4, 1, 2, 1, 1, 1, 2, 3, 7, 1, 2, 1, 1, 1, 2, 1, 12, 1, 2, 1, 1, 1, 2, 1, 5, 5, 2, 1, 1, 1, 2

Offset: 1

Author

Jaroslav Krizek, Mar 15 2009

Keywords

• nonn
• frac

Comments

Average of squares of the divisors of n = A001157(n)/A000005(n).

Iff a(n) = 1, n is in A020486.

Links

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

Crossrefs

Cf. A001157, A000005, A020486, A158299 (for numerators).

Programs

Mathematica

Array[Denominator[DivisorSigma[2, #]/DivisorSigma[0, #]] &, 100] (* Amiram Eldar, Jul 15 2019 *)

PARI

a(n) = denominator(sigma(n, 2)/numdiv(n)) \\ Michel Marcus, Jun 13 2013

Extensions

Data corrected and extended by Amiram Eldar, Jul 15 2019