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A120625
Numbers n such that the n-th Catalan number C(2n,n)/(n+1) is divisible by 3n.
2
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
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
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Jun 19 2006
EXTENSIONS
Definition corrected by Joel B. Lewis, Apr 30 2009
STATUS
approved