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A279290 Sum of cubes of nonprime divisors of n. 0
1, 1, 1, 65, 1, 217, 1, 577, 730, 1001, 1, 2009, 1, 2745, 3376, 4673, 1, 6778, 1, 9065, 9262, 10649, 1, 16345, 15626, 17577, 20413, 24761, 1, 31592, 1, 37441, 35938, 39305, 42876, 55226, 1, 54873, 59320, 73577, 1, 86310, 1, 95897, 95230, 97337, 1, 131033, 117650, 141626, 132652, 158249, 1, 183925, 166376 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

a(n) = 1 when n = 1 or n is prime.

a(p^k) = (p^(3*k+3) - 1)/(p^3 - 1) - p^3 for p is prime.

LINKS

Table of n, a(n) for n=1..55.

Index entries for sequences related to sums of divisors

FORMULA

a(n) = A001158(n) - A005064(n).

EXAMPLE

a(4) = 65 because 4 has 2 nonprime divisors {1,4} and 1^3 + 4^3 = 65.

MATHEMATICA

Table[DivisorSum[n, #1^3 & ,  !PrimeQ[#1] & ], {n, 55}]

Table[DivisorSigma[3, n] - DivisorSum[n, #1^3 & , PrimeQ[#1] & ], {n, 55}]

CROSSREFS

Cf. A001158, A005064, A023890, A189120.

Sequence in context: A087928 A204043 A295175 * A034061 A113696 A302210

Adjacent sequences:  A279287 A279288 A279289 * A279291 A279292 A279293

KEYWORD

nonn,easy

AUTHOR

Ilya Gutkovskiy, Dec 12 2016

STATUS

approved

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Last modified July 12 04:30 EDT 2020. Contains 335658 sequences. (Running on oeis4.)