A025248 a(n) = a(1)*a(n-1) + a(2)*a(n-2) + ...+ a(n-3)*a(3) for n >= 4.

1, 0, 2, 2, 2, 6, 14, 26, 58, 142, 326, 754, 1826, 4438, 10750, 26378, 65354, 162334, 405046, 1016546, 2561074, 6472550, 16415086, 41761786, 106526810, 272411054, 698275622, 1793763282, 4617047618, 11906277750, 30757124830, 79582907370, 206231537770

Offset

1,3

Links

Table of n, a(n) for n=1..33.

Formula

G.f.: (1+x-sqrt(1-2*x+x^2-8*x^3))/2. - Michael Somos, Jun 08 2000

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

Prog

(PARI) a(n)=polcoeff((x-sqrt(1-2*x+x^2-8*x^3+x*O(x^n)))/2, n)

Crossrefs

Sequence in context: A257255 A248765 A007039 * A213170 A321741 A101416

Adjacent sequences: A025245 A025246 A025247 * A025249 A025250 A025251

Keyword

nonn

Author

Clark Kimberling

Status

approved