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A027791 a(n) = 5*(n+1)*C(n+3,6). 1
20, 175, 840, 2940, 8400, 20790, 46200, 94380, 180180, 325325, 560560, 928200, 1485120, 2306220, 3488400, 5155080, 7461300, 10599435, 14805560, 20366500, 27627600, 37001250, 48976200, 64127700, 83128500 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,1

COMMENTS

Number of 10-subsequences of [ 1, n ] with just 3 contiguous pairs.

LINKS

Harvey P. Dale, Table of n, a(n) for n = 3..1000

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

FORMULA

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

a(n) = C(n+1, 4)*C(n+3, 3) - Zerinvary Lajos, May 10 2005, corrected by R. J. Mathar, Mar 16 2016

MATHEMATICA

Table[5(n+1)Binomial[n+3, 6], {n, 3, 30}] (* or *) LinearRecurrence[{8, -28, 56, -70, 56, -28, 8, -1}, {20, 175, 840, 2940, 8400, 20790, 46200, 94380}, 30] (* Harvey P. Dale, Nov 24 2015 *)

CROSSREFS

Sequence in context: A010826 A022712 A056128 * A047819 A163689 A140044

Adjacent sequences:  A027788 A027789 A027790 * A027792 A027793 A027794

KEYWORD

nonn

AUTHOR

thi ngoc dinh (via R. K. Guy)

STATUS

approved

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Last modified April 5 10:33 EDT 2020. Contains 333239 sequences. (Running on oeis4.)