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A372664
a(n) = Sum_{j=1..n} Sum_{k=1..n} phi(2*j*k) / phi(k).
1
1, 9, 21, 55, 93, 163, 241, 383, 507, 709, 915, 1205, 1497, 1907, 2220, 2794, 3306, 3966, 4610, 5438, 6075, 7113, 8067, 9245, 10272, 11742, 12900, 14552, 16086, 17798, 19552, 21894, 23532, 26082, 27933, 30589, 33105, 36307, 38619, 41945, 45049, 48459, 51875
OFFSET
1,2
LINKS
Eric Weisstein's World of Mathematics, Totient Function.
MATHEMATICA
Table[Sum[Sum[EulerPhi[2*j*k], {j, 1, n}]/EulerPhi[k], {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(k)));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, May 09 2024
STATUS
approved