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A137490 Numbers with 27 divisors. 1
900, 1764, 2304, 4356, 4900, 6084, 6400, 10404, 11025, 12100, 12544, 12996, 16900, 19044, 23716, 26244, 27225, 28900, 30276, 30976, 33124, 34596, 36100, 38025, 43264, 49284, 52900, 53361, 56644, 60516, 65025, 66564, 70756, 73984, 74529 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Maple implementation: see A030513.
Numbers of the form p^26 (subset of A089081), p^2*q^2*r^2 (like 900, 1764, 4356, squares of A007304) or p^2*q^8 (like 2304, 6400, subset of the squares of A030628) where p, q and r are distinct primes. - R. J. Mathar, Mar 01 2010
LINKS
FORMULA
A000005(a(n)) = 27.
Sum_{n>=1} 1/a(n) = (P(2)^3 + 2*P(6) - 3*P(2)*P(4))/6 + P(2)*P(8) - P(10) + P(26) = 0.00453941..., where P is the prime zeta function. - Amiram Eldar, Jul 03 2022
MATHEMATICA
Select[Range[150000], DivisorSigma[0, #]==27&] (* Vladimir Joseph Stephan Orlovsky, May 06 2011 *)
PROG
(PARI) isA137490(n) = numdiv(n)==27 \\ Michael B. Porter, Apr 10 2010
CROSSREFS
Sequence in context: A127658 A318720 A338540 * A129575 A328136 A336254
KEYWORD
nonn
AUTHOR
R. J. Mathar, Apr 22 2008
STATUS
approved

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Last modified March 19 01:57 EDT 2024. Contains 370952 sequences. (Running on oeis4.)