A372637 a(n) = (1/2) * Sum_{k=1..n} phi(6*k).

1, 3, 6, 10, 14, 20, 26, 34, 43, 51, 61, 73, 85, 97, 109, 125, 141, 159, 177, 193, 211, 231, 253, 277, 297, 321, 348, 372, 400, 424, 454, 486, 516, 548, 572, 608, 644, 680, 716, 748, 788, 824, 866, 906, 942, 986, 1032, 1080, 1122, 1162, 1210, 1258, 1310, 1364, 1404

Offset: 1

Author

Seiichi Manyama, May 08 2024

Keywords

• nonn

Links

• Eric Weisstein's World of Mathematics, Totient Function.

Crossrefs

Column k=6 of A372619.

Cf. A000010.

Programs

Mathematica

Accumulate[Table[EulerPhi[6*n], {n, 1, 60}]]/2 (* Amiram Eldar, May 08 2024 *)

PARI

a(n) = sum(k=1, n, eulerphi(6*k))/2;

Formula

a(n) ~ (9/(2*Pi^2)) * n^2. - Amiram Eldar, May 08 2024