A025246 - OEIS

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A025246

a(n) = a(1)*a(n-1) + a(2)*a(n-2) + ...+ a(n-3)*a(3) for n >= 4.

1, 0, 1, 1, 1, 2, 4, 7, 13, 26, 52, 104, 212, 438, 910, 1903, 4009, 8494, 18080, 38656, 82988, 178802, 386490, 837928, 1821664, 3970282, 8673258, 18987930, 41652382, 91539466, 201525238, 444379907, 981384125, 2170416738, 4806513660, 10657780276 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,6`
	COMMENTS	`Essentially the same as A023431.`
	LINKS	`INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 666`
	FORMULA	`G.f.: (1+x-sqrt(1-2x+x^2-4x^3))/2 - Michael Somos, Jun 08, 2000.`
	PROG	`(PARI) a(n)=polcoeff((1+x-sqrt(1-2x+x^2-4x^3+x*O(x^n)))/2, n)`
	CROSSREFS	`A023431(n)=a(n+3).` `Sequence in context: A099155 A068031 A023431 * A112740 A136408 A103104` `Adjacent sequences: A025243 A025244 A025245 * A025247 A025248 A025249`
	KEYWORD	`nonn`
	AUTHOR	`Clark Kimberling (ck6(AT)evansville.edu)`

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Last modified February 17 12:23 EST 2012. Contains 206011 sequences.