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A286764
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Total number of nodes summed over all lattice paths from (0,0) to (n,n) that do not go below the x-axis or above the diagonal x=y and consist of steps D=(1,-1), H=(1,0) and S=(0,1).
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2
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1, 3, 16, 109, 855, 7298, 65838, 617118, 5946781, 58506642, 584894463, 5921596628, 60565217546, 624644829720, 6487216108058, 67767838847144, 711463437534474, 7501409431304796, 79386836213817417, 842882477863610604, 8974911258934880498, 95806877080558096428
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OFFSET
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0,2
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LINKS
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FORMULA
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a(n) ~ c * phi^(5*n) / sqrt(n), where phi = A001622 is the golden ratio and c = 0.036755631845424682385214848270310481743236419858524834059514156934711202... - Vaclav Kotesovec, Sep 11 2021
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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$2],
(p-> p+[0, p[1]])(b(x-1, y)+b(x, y-1)+b(x-1, y+1))))
end:
a:= n-> b(n$2)[2]:
seq(a(n), n=0..30);
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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, 1}, Function[
p, p + {0, p[[1]]}][b[x - 1, y] + b[x, y - 1] + b[x - 1, y + 1]]]];
a[n_] := b[n, n][[2]];
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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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