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A317639
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Number of equivalence classes of Dyck paths of semilength n for the consecutive pattern UDUDD, where U=(1,1) and D=(1,-1).
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2
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1, 1, 1, 2, 4, 6, 10, 19, 32, 54, 98, 170, 292, 520, 909, 1577, 2787, 4883, 8515, 14998, 26299, 45984, 80863, 141844, 248381, 436406, 765649, 1341844, 2356500, 4134749, 7249981, 12728630, 22335110, 39174776, 68766785, 120670190, 211689586, 371558266, 652014636
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OFFSET
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0,4
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COMMENTS
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Two Dyck paths of the same length are equivalent with respect to a given pattern if they have equal sets of occurrences of this pattern.
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LINKS
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MAPLE
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b:= proc(x, y) option remember; `if`(y<0 or y>x, 0, `if`(x=0, 1,
`if`(y=0, b(x-2, y)+b(x-6, y+2), b(x-1, y-1))+b(x-5, y+1)))
end:
a:= n-> b(2*n, 0):
seq(a(n), n=0..42);
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MATHEMATICA
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b[x_, y_] := b[x, y] = If[y < 0 || y > x, 0, If[x == 0, 1, If[y == 0, b[x - 2, y] + b[x - 6, y + 2], b[x - 1, y - 1]] + b[x - 5, y + 1]]];
a[n_] := b[2n, 0];
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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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