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A094218 Number of permutations of length n with exactly 2 occurrences of the pattern 2-13. 8
0, 0, 0, 2, 25, 198, 1274, 7280, 38556, 193800, 937992, 4412826, 20309575, 91861770, 409704750, 1806342720, 7887861960, 34166674800, 146977222320, 628521016500, 2673950235138, 11324837666604, 47773836727540, 200828153398752 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,4
REFERENCES
R. Lie, Permutations and Patterns, Master's Thesis, Goeteborg, Sweden: Chalmers University of Technology, 2004.
LINKS
R. Parviainen, Lattice Path Enumeration of Permutations with k Occurrences of the Pattern 2-13, Journal of Integer Sequences, Vol. 9 (2006), Article 06.3.2.
FORMULA
a(n) = n*binomial(2*n,n-4)/2.
MATHEMATICA
Table[n Binomial[2 n, n - 4]/2, {n, 30}] (* Vincenzo Librandi, Aug 20 2015 *)
PROG
(PARI) a(n)=n*binomial(2*n, n-4)/2
(Magma) [n*Binomial(2*n, n-4)/2: n in [1..30]]; // Vincenzo Librandi, Aug 20 2015
CROSSREFS
Cf. A094219.
Column k=2 of A263776.
Sequence in context: A220276 A361874 A215298 * A203767 A206392 A074438
KEYWORD
nonn
AUTHOR
Benoit Cloitre, May 27 2004
STATUS
approved

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Last modified April 20 07:26 EDT 2024. Contains 371799 sequences. (Running on oeis4.)