A304575 - OEIS

A304575

a(n) = Sum_{d|n} #{k < d, k squarefree and relatively prime to d}.

1, 2, 3, 4, 4, 6, 6, 8, 7, 8, 8, 12, 9, 12, 12, 15, 12, 16, 13, 17, 16, 18, 16, 24, 17, 20, 20, 23, 18, 26, 20, 28, 23, 26, 24, 33, 24, 29, 28, 35, 27, 35, 29, 37, 34, 35, 31, 46, 32, 38, 35, 41, 33, 45, 36, 47, 38, 42, 37, 54, 38, 46, 46, 54, 42, 53, 42, 54

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OFFSET

1,2

COMMENTS

Note that a(n) <= n.

LINKS

Table of n, a(n) for n=1..68.

MATHEMATICA

s[n_]:=Length[Select[Range[n], And[SquareFreeQ[#], GCD[n, #]===1]&]];

Table[DivisorSum[n, s], {n, 100}]

PROG

(PARI) a(n) = sumdiv(n, d, #select(k->(issquarefree(k) && (gcd(k, d)==1)), [1..d])); \\ Michel Marcus, May 15 2018