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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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8
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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
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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.
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LINKS
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FORMULA
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a(n) = n*binomial(2*n,n-4)/2.
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MATHEMATICA
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PROG
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(PARI) a(n)=n*binomial(2*n, n-4)/2
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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