A025244 a(n) = a(1)*a(n-1) + a(2)*a(n-2) + ... + a(n-3)*a(3) for n >= 4.

1, 1, 2, 2, 4, 10, 22, 52, 130, 326, 832, 2162, 5674, 15032, 40178, 108154, 292956, 797994, 2184430, 6006028, 16579138, 45929838, 127656504, 355863330, 994735442, 2787537904, 7829586914, 22038759218, 62158281844, 175636481738, 497142172806, 1409444977380

Offset

1,3

Links

Table of n, a(n) for n=1..32.

Formula

G.f.: (1 + x + x^2 - sqrt(1 - 2*x - x^2 - 6*x^3 + x^4))/2. - Michael Somos, Jun 08 2000

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

Prog

(PARI) a(n)=polcoeff((x+x^2-sqrt(1-2*x-x^2-6*x^3+x^4+x*O(x^n)))/2, n)

Crossrefs

Sequence in context: A308986 A100088 A217212 * A132824 A298898 A339830

Adjacent sequences: A025241 A025242 A025243 * A025245 A025246 A025247

Keyword

nonn

Author

Clark Kimberling

Status

approved