A364212 - OEIS

%I #8 Jul 14 2023 09:04:02

%S 1,4,17,88,481,2812,16808,102988,640545,4035604,25679569,164778696,

%T 1064714401,6920652008,45214871857,296722645888,1954878268801,

%U 12923917765876,85705978837393,569944761286648,3799631728468936,25388448380261788,169992219503608177,1140364472585830196

%N a(n) = (1/(6*n)) * Sum_{d|n} 7^(n/d-1) * phi(7*d).

%F G.f.: (-1/6) * Sum_{k>0} phi(7*k) * log(1-7*x^k)/(7*k).

%t a[n_] := DivisorSum[n, 7^(n/#-1)*EulerPhi[7*#]/(6*n) &]; Array[a, 25] (* _Amiram Eldar_, Jul 14 2023 *)

%o (PARI) a(n) = sumdiv(n, d, 7^(n/d-1)*eulerphi(7*d))/(6*n);

%Y Cf. A000010, A359099, A359102.

%Y Cf. A000013, A364210, A364211.

%K nonn

%O 1,2

%A _Seiichi Manyama_, Jul 13 2023