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A027809 a(n) = 143*(n+1)*C(n+4,13)/2. 1

%I

%S 715,11011,90090,520520,2382380,9189180,31039008,94225560,261891630,

%T 675745070,1636014380,3747960216,8180071900,17103786700,34420042800,

%U 66927861000,126159017985,231196390425,412918656150,720279159600,1229442013800,2056876004040

%N a(n) = 143*(n+1)*C(n+4,13)/2.

%H T. D. Noe, <a href="/A027809/b027809.txt">Table of n, a(n) for n = 9..1000</a>

%F Number of 18-subsequences of [ 1, n ] with just 4 contiguous pairs.

%F G.f.: 143*(5+2x)*x^9/(1-x)^15.

%F a(n) = C(n+1, 10)*C(n+4, 4). - _Zerinvary Lajos_, May 26 2005, corrected by _R. J. Mathar_, Mar 16 2016

%t Table[143 (n + 1) Binomial[n + 4, 13]/2, {n, 9, 30}] (* or *) Table[Binomial[n + 1, 10] Binomial[n + 4, 4], {n, 9, 30}] (* _Michael De Vlieger_, Mar 16 2016 *)

%K nonn

%O 9,1

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

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Last modified August 10 12:19 EDT 2020. Contains 336379 sequences. (Running on oeis4.)