A372665 - OEIS

A372665

a(n) = Sum_{j=1..n} Sum_{k=1..n} phi(2*j*k) / phi(j*k).

1, 7, 14, 28, 41, 63, 82, 112, 137, 175, 206, 252, 289, 343, 386, 448, 497, 567, 622, 700, 761, 847, 914, 1008, 1081, 1183, 1262, 1372, 1457, 1575, 1666, 1792, 1889, 2023, 2126, 2268, 2377, 2527, 2642, 2800, 2921, 3087, 3214, 3388, 3521, 3703, 3842, 4032, 4177, 4375

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

Table of n, a(n) for n=1..50.

Eric Weisstein's World of Mathematics, Totient Function.

MATHEMATICA

Table[Sum[Sum[EulerPhi[2*j*k]/EulerPhi[j*k], {j, 1, n}], {k, 1, n}], {n, 1, 50}] (* Vaclav Kotesovec, May 09 2024 *)

PROG

(PARI) a(n) = sum(j=1, n, sum(k=1, n, eulerphi(2*j*k)/eulerphi(j*k)));

CROSSREFS

Cf. A000010, A372664.