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A030633 Numbers with 15 divisors. 9
144, 324, 400, 784, 1936, 2025, 2500, 2704, 3969, 4624, 5625, 5776, 8464, 9604, 9801, 13456, 13689, 15376, 16384, 21609, 21904, 23409, 26896, 29241, 29584, 30625, 35344, 42849, 44944, 55696, 58564, 59536, 60025, 68121, 71824, 75625 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers of the form p^14 (subset of A010802) or p^2*q^4 (A189988) where p and q are distinct primes. - R. J. Mathar, Mar 01 2010

LINKS

R. J. Mathar, Table of n, a(n) for n = 1..1000

FORMULA

From Amiram Eldar, Jul 03 2022: (Start)

A000005(a(n)) = 15.

Sum_{n>=1} 1/a(n) = P(2)*P(4) - P(6) + P(14) = 0.0178111..., where P is the prime zeta function. (End)

MATHEMATICA

Select[Range[300000], DivisorSigma[0, #]==15&] (* Vladimir Joseph Stephan Orlovsky, May 05 2011 *)

PROG

(PARI) is(n)=numdiv(n)==15 \\ Charles R Greathouse IV, Jun 19 2016

CROSSREFS

Cf. A000005, A010802, A030630, A030631, A030632, A189988.

Sequence in context: A154051 A335543 A217584 * A189988 A232892 A034285

Adjacent sequences:  A030630 A030631 A030632 * A030634 A030635 A030636

KEYWORD

nonn

AUTHOR

Jeff Burch

STATUS

approved

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Last modified August 10 08:49 EDT 2022. Contains 356039 sequences. (Running on oeis4.)