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Search: id:A094218
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| A094218 |
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Number of permutations of length n with exactly 2 occurrences of the pattern 2-13. |
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+0
7
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| 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; listen)
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OFFSET
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1,4
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REFERENCES
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R. Lie, Permutations and Patterns, Master's Thesis, Goeteborg, Sweden: Chalmers University of Technology, 2004.
Robert 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.
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FORMULA
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a(n)=n*(n-3)/2/(n+4)*binomial(2*n, n-3)
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PROGRAM
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(PARI) a(n)=n*(n-3)/2/(n+4)*binomial(2*n, n-3)
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CROSSREFS
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Cf. A094219.
Adjacent sequences: A094215 A094216 A094217 this_sequence A094219 A094220 A094221
Sequence in context: A009381 A063264 A024533 this_sequence A074438 A068176 A131585
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KEYWORD
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nonn
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AUTHOR
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Benoit Cloitre (benoit7848c(AT)orange.fr), May 27 2004
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