Voozh

A027802

a(n) = 5*(n+1)*binomial(n+4,6).

15, 140, 700, 2520, 7350, 18480, 41580, 85800, 165165, 300300, 520520, 866320, 1392300, 2170560, 3294600, 4883760, 7088235, 10094700, 14132580, 19481000, 26476450, 35521200, 47092500, 61752600, 80159625, 103079340, 131397840, 166135200, 208460120, 259705600

(list; graph; refs; listen; history; text; internal format)

OFFSET

2,1

COMMENTS

Number of 11-subsequences of [ 1, n ] with just 4 contiguous pairs.

LINKS

Table of n, a(n) for n=2..31.

Index entries for linear recurrences with constant coefficients, signature (8,-28,56,-70,56,-28,8,-1).

FORMULA

G.f.: 5*(3+4x)*x^2/(1-x)^8.

a(n) = C(n+1, 3)*C(n+4, 4) - Zerinvary Lajos, May 10 2005; corrected by R. J. Mathar, Feb 10 2016

From Amiram Eldar, Feb 04 2022: (Start)