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A027783 a(n) = 5*(n+1)*binomial(n+2,10). 1

%I

%S 45,550,3630,17160,65065,210210,600600,1555840,3719430,8314020,

%T 17551820,35271600,67897830,125847260,225544440,392251200,663966875,

%U 1096717050,1771619850,2804201400,4356527175,6652824750,9999397200,14809766400,21636143100,31208497320

%N a(n) = 5*(n+1)*binomial(n+2,10).

%H T. D. Noe, <a href="/A027783/b027783.txt">Table of n, a(n) for n = 8..1000</a>

%F Number of 13-subsequences of [ 1, n ] with just 2 contiguous pairs; g.f. 5*(9+2x)*x^8/(1-x)^12.

%F a(n) = C(n+1, 9)*C(n+2, 2). - _Zerinvary Lajos_, May 13 2005, corrected _R. J. Mathar_, Mar 15 2016

%t Table[5(n+1)Binomial[n+2,10],{n,8,30}] (* _Harvey P. Dale_, Jan 21 2012 *)

%K nonn,easy

%O 8,1

%A thi ngoc dinh (via _R. K. Guy_)

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Last modified June 19 17:25 EDT 2021. Contains 345144 sequences. (Running on oeis4.)