A120625 Numbers n such that the n-th Catalan number C(2n,n)/(n+1) is divisible by 3n.

15, 20, 42, 77, 88, 104, 126, 140, 153, 156, 170, 187, 190, 204, 209, 210, 220, 228, 231, 238, 240, 266, 299, 308, 312, 322, 368, 420, 429, 435, 440, 442, 450, 460, 464, 468, 476, 483, 493, 496, 510, 527, 551, 558, 561, 580, 589, 600, 609, 620, 624, 651, 665

Offset

1,1

Comments

Equivalently, numbers n such that the n-th central binomial coefficient C(2n,n) is divisible by 3n(n+1). - Joel B. Lewis, Jan 07 2008

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Mathematica

fQ[n_] := fQ[n_] := IntegerQ[ Binomial[2n, n]/(3n(n + 1))]; Select[ Range@681, fQ@# &]
With[{nn=700}, Transpose[Select[Thread[{CatalanNumber[Range[nn]], Range[ nn]}], Divisible[#[[1]], 3#[[2]]]&]][[2]]] (* Harvey P. Dale, Apr 30 2012 *)

Crossrefs

Subset of A104847, Cf. A120623.

Sequence in context: A065148 A093028 A105506 * A038352 A043125 A043905

Adjacent sequences: A120622 A120623 A120624 * A120626 A120627 A120628

Keyword

nonn

Author

Robert G. Wilson v, Jun 19 2006

Extensions

Definition corrected by Joel B. Lewis, Apr 30 2009

Status

approved