A349659 Sum of the nonrefactorable divisors of n.

0, 0, 3, 4, 5, 9, 7, 4, 3, 15, 11, 13, 13, 21, 23, 20, 17, 9, 19, 39, 31, 33, 23, 13, 30, 39, 30, 53, 29, 69, 31, 52, 47, 51, 47, 13, 37, 57, 55, 39, 41, 93, 43, 81, 68, 69, 47, 77, 56, 90, 71, 95, 53, 90, 71, 53, 79, 87, 59, 93, 61, 93, 94, 116, 83, 141, 67, 123, 95, 141, 71

Offset

1,3

Links

Table of n, a(n) for n=1..71.

Eric Weisstein's World of Mathematics, Refactorable Number

Formula

a(n) = A000203(n) - A335182(n).

a(p) = p for odd primes p. - Wesley Ivan Hurt, Nov 28 2021

Mathematica

a[n_] := DivisorSum[n, # &, !Divisible[#, DivisorSigma[0, #]] &]; Array[a, 100] (* Amiram Eldar, Nov 24 2021 *)

Prog

(PARI) a(n) = sumdiv(n, d, if (d%numdiv(d), d)); \\ Michel Marcus, Nov 24 2021

Crossrefs

Cf. A000203, A335182.

Sequence in context: A215496 A122401 A122403 * A302653 A300738 A324506

Adjacent sequences: A349656 A349657 A349658 * A349660 A349661 A349662

Keyword

nonn

Author

Wesley Ivan Hurt, Nov 23 2021

Status

approved