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A182886
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Triangle read by rows: T(n,k) is the number of weighted lattice paths in L_n having k (1,0)-steps. These are paths that start at (0,0), end on the horizontal axis and whose steps are of the following four kinds: a (1,0)-step with weight 1; a (1,0)-step with weight 2; a (1,1)-step with weight 2; a (1,-1)-step with weight 1. The weight of a path is the sum of the weights of its steps.
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2
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1, 0, 1, 0, 1, 1, 2, 0, 2, 1, 0, 6, 1, 3, 1, 0, 6, 12, 3, 4, 1, 6, 0, 24, 21, 6, 5, 1, 0, 30, 12, 60, 34, 10, 6, 1, 0, 30, 90, 60, 121, 52, 15, 7, 1, 20, 0, 180, 215, 76, 21, 8, 1, 0, 140, 90, 630, 540, 421, 351, 107, 28, 9, 1, 0, 140, 560, 630, 1710, 1176, 846, 539, 146, 36, 10, 1
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OFFSET
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0,7
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COMMENTS
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Sum of entries in row n is A051286(n).
T(3n,0) = binomial(2n,n) = A000984(n).
T(n,0) = 0 if n mod 3 > 0.
Sum_{k=0..n} k*T(n,k) = A182887(n).
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LINKS
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FORMULA
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G.f.: G(t,z) = 1/sqrt(1 - 2tz - 2tz^2 + t^2*z^2 + 2t^2*z^3 + t^2*z^4 - 4z^3).
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EXAMPLE
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T(3,2)=2. Indeed, denoting by h (H) the (1,0)-step of weight 1 (2), and u=(1,1), d=(1,-1), the five paths of weight 3 are ud, du, hH, Hh, and hhh; two of them, namely hH and Hh, have exactly two (1,0)-steps.
Triangle starts:
1;
0, 1;
0, 1, 1;
2, 0, 2, 1;
0, 6, 1, 3, 1;
0, 6, 12, 3, 4, 1;
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MAPLE
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G:=1/sqrt(1-2*t*z-2*t*z^2+t^2*z^2+2*t^2*z^3+t^2*z^4-4*z^3): Gser:=simplify(series(G, z=0, 14)): for n from 0 to 11 do P[n]:=sort(coeff(Gser, z, n)) od: for n from 0 to 11 do seq(coeff(P[n], t, k), k=0..n) 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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