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A094218 Number of permutations of length n with exactly 2 occurrences of the pattern 2-13. 8

%I

%S 0,0,0,2,25,198,1274,7280,38556,193800,937992,4412826,20309575,

%T 91861770,409704750,1806342720,7887861960,34166674800,146977222320,

%U 628521016500,2673950235138,11324837666604,47773836727540,200828153398752

%N Number of permutations of length n with exactly 2 occurrences of the pattern 2-13.

%D R. Lie, Permutations and Patterns, Master's Thesis, Goeteborg, Sweden: Chalmers University of Technology, 2004.

%H Alois P. Heinz, <a href="/A094218/b094218.txt">Table of n, a(n) for n = 1..500</a>

%H R. Parviainen, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL9/Parviainen/parviainen3.html">Lattice Path Enumeration of Permutations with k Occurrences of the Pattern 2-13</a>, Journal of Integer Sequences, Vol. 9 (2006), Article 06.3.2.

%F a(n) = n*binomial(2*n,n-4)/2.

%t Table[n Binomial[2 n, n - 4]/2, {n, 30}] (* _Vincenzo Librandi_, Aug 20 2015 *)

%o (PARI) a(n)=n*binomial(2*n,n-4)/2

%o (MAGMA) [n*Binomial(2*n,n-4)/2: n in [1..30]]; // _Vincenzo Librandi_, Aug 20 2015

%Y Cf. A094219.

%Y Column k=2 of A263776.

%K nonn

%O 1,4

%A _Benoit Cloitre_, May 27 2004

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Last modified March 31 16:23 EDT 2020. Contains 333151 sequences. (Running on oeis4.)