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A027788 a(n) = 15*(n+1)*C(n+2,15)/2. 1
105, 1800, 16320, 104040, 523260, 2209320, 8139600, 26860680, 80901810, 225544440, 588376800, 1448655000, 3389852700, 7582037400, 16287339600, 33738060600, 67621543875, 131530532400, 248917996800, 459351961200, 828225505800, 1461574422000, 2528333935200 (list; graph; refs; listen; history; text; internal format)
OFFSET

13,1

COMMENTS

Number of 18-subsequences of [ 1, n ] with just 2 contiguous pairs.

LINKS

T. D. Noe, Table of n, a(n) for n = 13..1000

FORMULA

G.f.: 15*(7+x)*x^13/(1-x)^17.

a(n) = C(n+1, 14)*C(n+2, 2). - Zerinvary Lajos, Apr 28 2005, corrected by R. J. Mathar, Mar 16 2016

MATHEMATICA

Table[15 (n + 1) Binomial[n + 2, 15]/2, {n, 13, 40}] (* or *) Table[Binomial[n + 1, 14] Binomial[n + 2, 2], {n, 13, 40}] (* Michael De Vlieger, Mar 16 2016 *)

CROSSREFS

Sequence in context: A076377 A165374 A024198 * A112497 A220822 A166821

Adjacent sequences:  A027785 A027786 A027787 * A027789 A027790 A027791

KEYWORD

nonn

AUTHOR

thi ngoc dinh (via R. K. Guy)

STATUS

approved

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Last modified April 8 02:27 EDT 2020. Contains 333312 sequences. (Running on oeis4.)