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A025256 a(n) = a(1)*a(n-1) + a(2)*a(n-2) + ...+ a(n-3)*a(3) for n >= 4. 1
1, 1, 3, 3, 6, 18, 42, 105, 291, 792, 2181, 6177, 17628, 50679, 147255, 430917, 1268292, 3754926, 11172828, 33389040, 100181994, 301682709, 911436117, 2761852011, 8392005462, 25563691341, 78053071611, 238830914937, 732247187460, 2249217635238 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..30.

FORMULA

G.f.: (1+x+x^2-sqrt(1-2*x-x^2-10*x^3+x^4))/2. - Vladeta Jovovic, May 07 2003

Conjecture: n*a(n) +(-2*n+3)*a(n-1) +(-n+3)*a(n-2) +5*(-2*n+9)*a(n-3) +(n-6)*a(n-4)=0. - R. J. Mathar, Feb 25 2015

MATHEMATICA

CoefficientList[Series[(1+x+x^2-Sqrt[(1-2x-x^2-10x^3+x^4)])/2, {x, 0, 40}], x] (* Harvey P. Dale, Aug 31 2020 *)

CROSSREFS

Sequence in context: A123286 A132818 A134068 * A052560 A147836 A284710

Adjacent sequences:  A025253 A025254 A025255 * A025257 A025258 A025259

KEYWORD

nonn

AUTHOR

Clark Kimberling

STATUS

approved

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Last modified November 25 14:33 EST 2020. Contains 338624 sequences. (Running on oeis4.)