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A105929
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Triangle read by rows: T(n,k) is the number of directed column-convex polyominoes of area n, having k columns of height 1 starting at level 0.
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0
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1, 0, 1, 1, 0, 1, 2, 2, 0, 1, 6, 3, 3, 0, 1, 16, 9, 4, 4, 0, 1, 43, 22, 13, 5, 5, 0, 1, 114, 58, 30, 18, 6, 6, 0, 1, 301, 151, 79, 40, 24, 7, 7, 0, 1, 792, 396, 202, 107, 52, 31, 8, 8, 0, 1, 2080, 1038, 526, 270, 143, 66, 39, 9, 9, 0, 1, 5456, 2722, 1370, 701, 358, 188, 82, 48, 10, 10
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OFFSET
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0,7
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COMMENTS
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T(n,k) is the number of nondecreasing Dyck paths of semilength n, having k peaks at height 1. Example: T(4,2)=3 because we have UDUDUUDD, UDUUDDUD and UUDDUDUD, where U=(1,1) and D=(1,-1). sum(T(n,k),k=0..n)=fibonacci(2n-1) (A001519). sum(k*T(n,k),k=0..n)=fibonacci(2n-1) (A001519). T(n,0)=A027994(n-2) for n>=2.
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REFERENCES
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E. Deutsch and H. Prodinger, A bijection between directed column-convex polyominoes and ordered trees of height at most three, Theoretical Comp. Science, 307, 2003, 319-325.
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LINKS
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FORMULA
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G.f.=(1-2z)^2/[(1-3z+z^2)(1-z-z^2-tz+tz^2)].
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EXAMPLE
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Triangle begins:
1;
0,1;
1,0,1;
2,2,0,1;
6,3,3,0,1;
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MAPLE
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G:=(1-2*z)^2/(1-3*z+z^2)/(1-z-z^2-t*z+t*z^2):Gser:=simplify(series(G, z=0, 14)): P[0]:=1: for n from 1 to 12 do P[n]:=coeff(Gser, z^n) od: for n from 0 to 12 do seq(coeff(t*P[n], t^k), k=1..n+1) od; # yields sequence in triangular form
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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