OFFSET
1,4
FORMULA
a(n) = Sum_{d|n, nonprime d, n/d squarefree} d.
EXAMPLE
a(8) = 12. The nonprime divisors of 8 whose divisor complements are squarefree are 4 and 8 and their sum is 12.
MATHEMATICA
a[n_] := DivisorSum[n, # &, ! PrimeQ[#] && SquareFreeQ[n/#] &]; Array[a, 100] (* Amiram Eldar, Oct 30 2022 *)
PROG
(PARI) a(n) = sumdiv(n, d, if (!isprime(d) && issquarefree(n/d), d)); \\ Michel Marcus, Oct 30 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Wesley Ivan Hurt, Oct 29 2022
STATUS
approved