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A264455
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Number of permutations of [n] with exactly six (possibly overlapping) occurrences of the generalized pattern 12-3.
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2
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1, 17, 238, 2956, 33343, 355182, 3681762, 37839385, 389940538, 4056942189, 42796503464, 458995025669, 5013561835833, 55832699192796, 634322118799677, 7354538207075076, 87032355679553323, 1051183375285792257, 12956782873283747998, 162950022525866642259
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OFFSET
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5,2
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LINKS
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EXAMPLE
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a(5) = 1: 12345.
a(6) = 17: 124365, 124635, 124653, 125346, 132456, 134256, 134526, 134562, 213456, 231456, 234156, 234516, 234561, 312456, 412356, 512346, 612345.
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MAPLE
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b:= proc(u, o) option remember; `if`(u+o=0, 1, add(
b(u-j, o+j-1), j=1..u)+add(convert(series(
b(u+j-1, o-j)*x^(o-j), x, 7), polynom), j=1..o))
end:
a:= n-> coeff(b(n, 0), x, 6):
seq(a(n), n=5..25);
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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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