A348060 - OEIS

%I #9 Sep 27 2021 07:28:19

%S 0,0,1,1,6,2,15,5,15,8,45,7,66,18,30,21,120,18,153,23,70,50,231,24,

%T 190,72,147,56,378,40,435,85,194,128,280,55,630,162,284,87,780,68,861,

%U 153,264,242,1035,91,861,200,502,213,1326,156,788,205,642,392,1653,110,1770,450,606,341,1136

%N a(n) = Sum_{k=1..n, gcd(n,k) = 1} (k-1) / gcd(n,k-1).

%t Table[Sum[If[GCD[n, k] == 1, (k - 1)/GCD[n, k - 1], 0], {k, n}], {n, 65}]

%o (PARI) a(n) = sum(k=1, n, if (gcd(n, k)==1, (k-1)/gcd(n, k-1))); \\ _Michel Marcus_, Sep 27 2021

%Y Cf. A057661, A062355, A348061.

%K nonn

%O 1,5

%A _Ilya Gutkovskiy_, Sep 26 2021