A007517 a(n) = phi(n) * (sigma(n) - n).

0, 1, 2, 6, 4, 12, 6, 28, 24, 32, 10, 64, 12, 60, 72, 120, 16, 126, 18, 176, 132, 140, 22, 288, 120, 192, 234, 336, 28, 336, 30, 496, 300, 320, 312, 660, 36, 396, 408, 800, 40, 648, 42, 800, 792, 572, 46, 1216, 336, 860, 672, 1104, 52, 1188, 680

Offset: 1

Author

Walter Nissen

Keywords

• nonn
• easy

Links

• G. C. Greubel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000010, A000203, A001065, A059956, A065465.

Programs

GAP

List([1..60],n->Phi(n)*(Sigma(n)-n)); # Muniru A Asiru, Mar 22 2018

Maple

with(numtheory): seq(phi(n)*(sigma(n)-n),n=1..60); # Muniru A Asiru, Mar 22 2018

Mathematica

Table[EulerPhi[n](DivisorSigma[1,n]-n),{n,60}] (* Harvey P. Dale, Mar 16 2013 *)

PARI

for(n=1,50, print1(eulerphi(n)*(sigma(n) - n), ", ")) \\ G. C. Greubel, Mar 22 2018

Formula

a(n) = A000010(n)*A001065(n). - Michel Marcus, Mar 22 2018

Sum_{k=1..n} a(k) ~ c * n^2 / 3, where c = A065465 - A059956 = 0.273586... . - Amiram Eldar, Dec 04 2023