OFFSET
1,2
LINKS
Vaclav Kotesovec, Table of n, a(n) for n = 1..10000
Vaclav Kotesovec, Plot of a(n)/n^4 for n = 1..100000
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