A071721 - OEIS

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A071721

Expansion of (1+x^2*C^2)*C^2, where C = (1-(1-4*x)^(1/2))/(2*x) is g.f. for Catalan numbers, A000108.

1, 2, 6, 18, 56, 180, 594, 2002, 6864, 23868, 83980, 298452, 1069776, 3863080, 14040810, 51325650, 188574240, 695987820, 2579248980, 9593714460, 35804293200, 134032593240, 503154100020, 1893689067348, 7144084508256 (list; graph; refs; listen; history; internal format)

	OFFSET	`0,2`
	COMMENTS	`A071721(n) = A138156(n) - 4*A138156(n-1) - Alzhekeyev Ascar M, Jul 19 2011`
	FORMULA	`a(n) = 6n * (2n)! / [(n+2)n!(n+1)! ], n>0. In terms of Catalan numbers (A000108), a(n) = 6n*Cat(n)/(n+2), n>0. - Ralf Stephan, Mar 11 2004`
	CROSSREFS	`Cf. A002421.` `Sequence in context: A091142 A111961 A190861 * A125306 A064310 A126983` `Adjacent sequences: A071718 A071719 A071720 * A071722 A071723 A071724`
	KEYWORD	`nonn`
	AUTHOR	`N. J. A. Sloane (njas(AT)research.att.com), Jun 06 2002`

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Last modified February 15 08:49 EST 2012. Contains 205740 sequences.