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A372633
a(n) = Sum_{j=1..n} Sum_{k=1..n} phi(j*k).
6
1, 5, 19, 47, 115, 183, 369, 585, 927, 1271, 2021, 2557, 3817, 4813, 6101, 7749, 10581, 12381, 16395, 19147, 22855, 26795, 33901, 38141, 46081, 52729, 61711, 69487, 83851, 90731, 108341, 121749, 136929, 152065, 171097, 185257, 215101, 236377, 261553, 283153, 323993
OFFSET
1,2
LINKS
Eric Weisstein's World of Mathematics, Totient Function.
FORMULA
a(n) ~ c * n^4, where c = A065464 / 4 = 0.107062376419... . - Amiram Eldar, May 09 2024
MATHEMATICA
Table[Sum[EulerPhi[i*j], {i, 1, n}, {j, 1, n}], {n, 1, 50}] (* Vaclav Kotesovec, May 08 2024 *)
s = 1; Join[{1}, Table[s += EulerPhi[n^2] + 2*Sum[EulerPhi[j*n], {j, 1, n-1}], {n, 2, 50}]] (* Vaclav Kotesovec, May 08 2024 *)
PROG
(PARI) a(n) = sum(j=1, n, sum(k=1, n, eulerphi(j*k)));
CROSSREFS
KEYWORD
nonn,nice
AUTHOR
Seiichi Manyama, May 08 2024
STATUS
approved