A163372 a(n) = sigma(phi(sigma(n))).

1, 3, 3, 12, 3, 7, 7, 15, 28, 12, 7, 28, 12, 15, 15, 72, 12, 60, 15, 28, 31, 28, 15, 31, 72, 28, 31, 60, 15, 60, 31, 91, 31, 39, 31, 195, 39, 31, 60, 60, 28, 63, 42, 60, 60, 60, 31, 168, 91, 168, 60, 96, 39, 63, 60, 63, 63, 60, 31, 124, 72, 63, 124, 312, 60, 124

Offset: 1

Author

Jaroslav Krizek, Jul 25 2009

Keywords

• nonn

Links

• G. C. Greubel, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000010, A000203, A062401, A062402.

Programs

Magma

[SumOfDivisors(EulerPhi(SumOfDivisors(n))): n in [1..80]]; // Vincenzo Librandi, Dec 20 2016

Maple

with(numtheory): A163372:=n->sigma(phi(sigma(n))): seq(A163372(n), n=1..100); # Wesley Ivan Hurt, Oct 06 2017

Mathematica

DivisorSigma[1, EulerPhi[DivisorSigma[1, Range[100]]]] (* G. C. Greubel, Dec 20 2016 *)

PARI

vector(80, n, sigma(eulerphi(sigma(n)))) \\ Michel Marcus, Jul 31 2015

Formula

a(n) = A000203(A000010(A000203(n))) = A000203(A062401(n)) = A062402(A000203(n)).

Extensions

More terms from Michel Marcus, Jul 31 2015