OFFSET
1,2
FORMULA
a(n) = n * Sum_{d|n, d<=sqrt(n)} mu(d)^2 / d.
EXAMPLE
a(16) = 16 * Sum_{d|16, d<=sqrt(16)} mu(d)^2 / d = 16 * (mu(1)^2/1 + mu(2)^2/2) = 16 * (1 + 1/2) = 24.
MATHEMATICA
a[n_] := DivisorSum[n, n/# &, #^2 <= n && SquareFreeQ[#] &]; Array[a, 100] (* Amiram Eldar, May 25 2023 *)
PROG
(PARI) a(n) = sumdiv(n, d, if (issquarefree(d) && (d^2 <= n), n/d)); \\ Michel Marcus, May 25 2023
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wesley Ivan Hurt, May 25 2023
STATUS
approved