A030232 Numbers k such that the number of divisors of k! divides the number of divisors of (2k)!.

1, 2, 4, 8, 10, 13, 20, 22, 24, 32, 33, 34, 37, 42, 56, 68, 75, 100, 102, 108, 114, 129, 133, 134, 136, 148, 149, 153, 159, 161, 162, 186, 187, 248, 249, 254, 277, 300, 301, 310, 311, 330, 331, 351, 380, 381, 382, 388, 411, 423, 430, 488, 489, 531, 545, 556

Offset

1,2

Comments

Numbers k such that A000005(k!) divides A000005((2k)!).

Links

Amiram Eldar, Table of n, a(n) for n = 1..121

Mathematica

Select[Range[560], Divisible[DivisorSigma[0, (2#)!], DivisorSigma[ 0, #!]]&] (* Harvey P. Dale, Mar 06 2015 *)

Prog

(PARI) isok(n) = (numdiv((2*n)!) % numdiv(n!)) == 0; \\ Michel Marcus, Apr 16 2015

Crossrefs

Cf. A000005 (number of divisors), A027423 (number of divisors of n!).

Sequence in context: A141400 A190744 A190751 * A102024 A104197 A323440

Adjacent sequences: A030229 A030230 A030231 * A030233 A030234 A030235

Keyword

easy,nonn

Author

Benoit Cloitre, Sep 28 2002

Status

approved