A070763 - OEIS

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A070763

Numbers n such that sigma(n) is a power of prime (of the form p^a, p prime, a>=1).

2, 3, 4, 7, 9, 16, 21, 25, 31, 64, 81, 93, 127, 217, 289, 381, 400, 651, 729, 889, 1681, 2401, 2667, 3481, 3937, 4096, 5041, 7921, 8191, 10201, 11811, 15625, 17161, 24573, 27559, 27889, 28561, 29929, 57337, 65536, 82677, 83521, 85849

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OFFSET

1,1

COMMENTS

Contains all Mersenne primes (A000668) and squarefree products thereof (A046528 except 1). - Ivan Neretin, Feb 08 2017

LINKS

Ivan Neretin, Table of n, a(n) for n = 1..10000

EXAMPLE

sigma(57337)=2^16 hence 57337 is in the sequence.

MATHEMATICA

Select[Range[100000], PrimePowerQ[DivisorSigma[1, #]] &] (* Ivan Neretin, Feb 08 2017 *)

PROG

(PARI) for(n=1, 100000, if(omega(sigma(n)) == 1, print1(n, ", ")))

CROSSREFS

Cf. A071114.

Sequence in context: A067236 A320357 A250255 * A295619 A319645 A071114

Adjacent sequences: A070760 A070761 A070762 * A070764 A070765 A070766

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, May 14 2002

STATUS

approved