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A137488 Numbers with 25 divisors. 7
1296, 10000, 38416, 50625, 194481, 234256, 456976, 1185921, 1336336, 1500625, 2085136, 2313441, 4477456, 6765201, 9150625, 10556001, 11316496, 14776336, 16777216, 17850625, 22667121, 29986576, 35153041, 45212176, 52200625 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Maple implementation: see A030513.
Numbers of the form p^24 (24th powers of A000040, subset of A010812) or p^4*q^4 (A189991), where p and q are distinct primes. - R. J. Mathar, Mar 01 2010
LINKS
FORMULA
A000005(a(n)) = 25.
Sum_{n>=1} 1/a(n) = (P(4)^2 - P(8))/2 + P(24) = 0.000933328..., where P is the prime zeta function. - Amiram Eldar, Jul 03 2022
MATHEMATICA
lst = {}; Do[If[DivisorSigma[0, n] == 25, Print[n]; AppendTo[lst, n]], {n, 55000000}]; lst (* Vladimir Joseph Stephan Orlovsky, May 03 2011 *)
Select[Range[5221*10^4], DivisorSigma[0, #]==25&] (* Harvey P. Dale, Mar 11 2019 *)
PROG
(Haskell)
a137488 n = a137488_list !! (n-1)
a137488_list = m (map (^ 24) a000040_list) (map (^ 4) a006881_list) where
m xs'@(x:xs) ys'@(y:ys) | x < y = x : m xs ys'
| otherwise = y : m xs' ys
-- Reinhard Zumkeller, Nov 29 2011
(PARI) is(n)=numdiv(n)==25 \\ Charles R Greathouse IV, Jun 19 2016
CROSSREFS
Sequence in context: A250810 A320893 A276282 * A189991 A250438 A221006
KEYWORD
nonn
AUTHOR
R. J. Mathar, Apr 22 2008
STATUS
approved

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Last modified July 19 01:31 EDT 2024. Contains 374388 sequences. (Running on oeis4.)