A058008 Numbers k such that (2*k - 1)!/(k!)^2 is an integer.

1, 6, 15, 28, 42, 45, 66, 77, 91, 110, 126, 140, 153, 156, 170, 187, 190, 204, 209, 210, 220, 228, 231, 238, 266, 276, 299, 308, 312, 315, 322, 325, 330, 345, 378, 414, 420, 429, 435, 440, 442, 450, 459, 460, 468, 476, 483, 493, 496

Offset

1,2

Comments

Original name was: Numbers n such that gcd(2*n,C(2*n,n))=2*n.

For n a prime power (see A000961) we have gcd(2*n,C(2*n,n))=2. - Arkadiusz Wesolowski, Jul 01 2012

Also, positions where A075055 differs from A000984. - Ralf Stephan, Dec 11 2004

Links

Giovanni Resta, Table of n, a(n) for n = 1..10000

Formula

Appears to be A067348(n)/2. - Benoit Cloitre, Mar 21 2003

Terms >1 are given by A002503+1. - Benoit Cloitre, Dec 09 2017

Mathematica

Select[Range[500], IntegerQ[(2 # - 1)!/#!^2] &] (* Arkadiusz Wesolowski, Jul 01 2012 *)

Crossrefs

Cf. A000961, A001405, A002503, A075055, A000984, A067348.

Sequence in context: A117519 A091012 A241988 * A094142 A081873 A096892

Adjacent sequences: A058005 A058006 A058007 * A058009 A058010 A058011

Keyword

nonn

Author

Labos Elemer, Nov 13 2000

Extensions

Name changed by Arkadiusz Wesolowski, Jul 01 2012

Status

approved