A088662 - OEIS

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A088662

Number of peaks at even level in all symmetric Dyck paths of semilength n+2.

1, 2, 7, 12, 34, 60, 155, 280, 686, 1260, 2982, 5544, 12804, 24024, 54483, 102960, 230230, 437580, 967538, 1847560, 4047836, 7759752, 16871582, 32449872, 70100044, 135207800, 290473900, 561632400, 1200823560, 2326762800 (list; graph; refs; listen; history; internal format)

	OFFSET	`0,2`
	FORMULA	`G.f.=(1-2z+4z^3)/[2z^2(1-2z)sqrt(1-4z^2)]-1/(2z^2). a(2n)=(2n)!(2n^2+4n+1)/[n!(n+1)! ], a(2n+1)=2(2n+1)!/(n!)^2. a(2n+1)=2A002457(n).`
	CROSSREFS	`Cf. A002457.` `Sequence in context: A007230 A059053 A032025 * A073710 A092831 A055257` `Adjacent sequences: A088659 A088660 A088661 * A088663 A088664 A088665`
	KEYWORD	`nonn`
	AUTHOR	`Emeric Deutsch (deutsch(AT)duke.poly.edu), Nov 21 2003`

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Last modified February 17 19:07 EST 2012. Contains 206085 sequences.