A163108 a(n) = sigma(tau(sigma(n))).

1, 3, 4, 3, 7, 12, 7, 7, 3, 12, 12, 12, 7, 15, 15, 3, 12, 7, 12, 15, 12, 13, 15, 28, 3, 15, 15, 15, 15, 28, 12, 12, 18, 15, 18, 7, 7, 28, 15, 28, 15, 28, 12, 28, 15, 28, 18, 12, 7, 7, 28, 12, 15, 31, 28, 31, 18, 28, 28, 31, 7, 28, 15, 3, 28, 24, 12, 28, 28, 24, 28, 15, 7, 15, 12, 28, 28

Offset: 1

Author

Jaroslav Krizek, Jul 20 2009

Keywords

• nonn

Comments

Repeated application of tau (number of divisors) and sigma (sum of divisors).

Links

• Antti Karttunen, Table of n, a(n) for n = 1..16384
• Index entries for sequences related to sigma(n)

Crossrefs

Cf. A000005, A000203, A062068, A062069, A163107.

Programs

Maple

with(numtheory) : A163108 := proc(n) sigma(tau(sigma(n))) ; end: seq(A163108(n),n=1..120) ; # R. J. Mathar, Jul 27 2009

PARI

A163108(n) = sigma(numdiv(sigma(n))); \\ Antti Karttunen, Nov 18 2017

Formula

a(n) = A000203(A000005(A000203(n))) = A000203(A062068(n)) = A062069(A000203(n)).

Extensions

More terms from R. J. Mathar, Jul 27 2009