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A133477 Sum of cubefree divisors of n excluding 1. 1
0, 2, 3, 6, 5, 11, 7, 6, 12, 17, 11, 27, 13, 23, 23, 6, 17, 38, 19, 41, 31, 35, 23, 27, 30, 41, 12, 55, 29, 71, 31, 6, 47, 53, 47, 90, 37, 59, 55, 41, 41, 95, 43, 83, 77, 71, 47, 27, 56, 92, 71, 97, 53, 38, 71, 55, 79, 89, 59, 167, 61, 95, 103, 6, 83, 143, 67, 125, 95, 143, 71, 90 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
FORMULA
a(n) = A073185(n) - 1. - N. J. A. Sloane, Nov 30 2007
EXAMPLE
a(8) = 6 because the divisors of 8 are {1,2,4,8}, the cubefree divisors are 1, 2, 4 so we get a(8) = 2 + 4 = 6.
MATHEMATICA
scfd[n_]:=Total[Select[Divisors[n], Max[Transpose[FactorInteger[#]][[2]]]<3&]]; Array[scfd, 80]-1 (* Harvey P. Dale, Nov 30 2014 *)
f[p_, e_] := 1 + p + If[e > 1, p^2, 0]; a[1] = 0; a[n_] := -1 + Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* Amiram Eldar, Jul 09 2022 *)
CROSSREFS
Sequence in context: A274608 A319680 A350337 * A303695 A345321 A350339
KEYWORD
easy,nonn
AUTHOR
Jonathan Vos Post, Nov 29 2007
EXTENSIONS
Edited by N. J. A. Sloane, Nov 30 2007
STATUS
approved

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Last modified March 29 09:59 EDT 2024. Contains 371268 sequences. (Running on oeis4.)