A015763 - OEIS

A015763

Numbers k such that phi(k) divides sigma_5(k).

1, 2, 3, 6, 12, 14, 15, 30, 35, 42, 46, 56, 70, 78, 105, 134, 138, 140, 161, 168, 184, 190, 210, 230, 248, 264, 270, 299, 322, 357, 402, 414, 418, 420, 483, 552, 570, 594, 598, 616, 623, 630, 644, 670, 690, 714, 744, 805, 812, 840, 874, 897, 910

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

COMMENTS

sigma_5(n) is the sum of the 5th powers of the divisors of n.

LINKS

David A. Corneth, Table of n, a(n) for n = 1..10000

EXAMPLE

sigma_5(12) = 1^5 + 2^5 + 3^5 + 4^5 + 6^5 + 12^5 = 257908. phi(12) = 4. sigma_5(12) = 257908 is divisible by phi(12) = 4 so 12 is in the sequence. - David A. Corneth, Aug 24 2019

MATHEMATICA

Select[Range[910], Divisible[DivisorSigma[5, #], EulerPhi[#]] &] (* Jon Maiga, Aug 24 2019 *)

PROG

(PARI) isok(n) = !(sigma(n, 5) % eulerphi(n)); \\ Michel Marcus, Aug 24 2019

(Magma) [k:k in [1..1000]| DivisorSigma(5, k) mod EulerPhi(k) eq 0]; // Marius A. Burtea, Aug 24 2019

CROSSREFS

Cf. A000010, A001160.

Sequence in context: A015774 A015767 A015761 * A015769 A015765 A015771

Adjacent sequences: A015760 A015761 A015762 * A015764 A015765 A015766

KEYWORD

nonn,easy

AUTHOR

Robert G. Wilson v

STATUS

approved