OFFSET
1,2
LINKS
Eric Weisstein's World of Mathematics, Totient Function.
FORMULA
a(n) ~ (25/(8*Pi^2)) * n^2. - Amiram Eldar, May 08 2024
MATHEMATICA
Accumulate[Table[EulerPhi[5*n], {n, 1, 60}]]/4 (* Amiram Eldar, May 08 2024 *)
PROG
(PARI) a(n) = sum(k=1, n, eulerphi(5*k))/4;
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, May 07 2024
STATUS
approved