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A121467
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Triangle read by rows: T(n,k) is the number of nondecreasing Dyck paths of semilength n and area k (n>=1, k>=1).
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1
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1, 0, 1, 0, 1, 0, 0, 1, 0, 2, 0, 1, 0, 1, 0, 0, 0, 1, 0, 3, 0, 2, 0, 3, 0, 2, 0, 1, 0, 1, 0, 0, 0, 0, 1, 0, 4, 0, 4, 0, 5, 0, 5, 0, 4, 0, 4, 0, 3, 0, 2, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 5, 0, 7, 0, 8, 0, 10, 0, 8, 0, 11, 0, 9, 0, 7, 0, 6, 0, 6, 0, 4, 0, 3, 0, 2, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 6, 0, 11, 0, 13
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OFFSET
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1,10
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COMMENTS
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Row n has n^2 terms. Row sums are the odd-subscripted Fibonacci numbers (A001519). Sum(k*T(n,k),k=1..n^2)=A061648(n).
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LINKS
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FORMULA
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G.f.: G(q,x)=Sum(F[n]x^n, n>=0), where the q-analogs F[n] of the Fibonacci numbers are defined by F[0]=0, F[1]=q, F[n+2]=F[n+1]q^(2n+3)+Sum(F[n-k+1]q^((k+1)^2),k=0..n).
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EXAMPLE
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T(3,5)=2 because we have UDUUDD and UUDDUD, where U=(1,1) and D(1,-1).
Triangle starts:
1;
0,1,0,1;
0,0,1,0,2,0,1,0,1;
0,0,0,1,0,3,0,2,0,3,0,2,0,1,0,1;
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MAPLE
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P[1]:=q: for n from 2 to 10 do P[n]:=sort(expand(q^(2*n-1)*P[n-1]+sum(q^((k+1)^2)*P[n-k-1], k=0..n-2))) od: for n from 1 to 7 do seq(coeff(P[n], q, j), j=1..n^2) od; # yields sequence in triangular form
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CROSSREFS
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KEYWORD
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nonn,tabf
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AUTHOR
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STATUS
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approved
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