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URL: https://oeis.org/A247748

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A247748
Total area below all lattice paths from (0,0) to (n,0) that do not go below the x-axis or above the diagonal x=y and consist of steps u=(1,1), U=(1,3), H=(1,0), d=(1,-1) and D=(1,-3).
3
0, 0, 1, 4, 29, 128, 683, 3048, 15631, 73584, 367878, 1766272, 8772765, 42778568, 212026492, 1041894304, 5164955809, 25511089124, 126587331646, 627213797064, 3115744498691, 15471098709336, 76936461658184, 382598697899276, 1904401873987964, 9480893249387192
OFFSET
0,4
LINKS
FORMULA
a(n) = Sum_{k>=1} k * A247749(n,k).
MAPLE
b:= proc(x, y) option remember; `if`(y<0 or x<y, 0,
`if`(x=0, [1, 0], add((p->p+[0, p[1]*(y+j/2)])
(b(x-1, y+j)), j=[-1, -3, 0, 1, 3])))
end:
a:= n-> b(n, 0)[2]:
seq(a(n), n=0..30);
MATHEMATICA
b[x_, y_] := b[x, y] = If[y < 0 || x < y, {0, 0},
If[x == 0, {1, 0}, Sum[Function[p, p + {0, p[[1]]*(y + j/2)}][
b[x - 1, y + j]], {j, {-1, -3, 0, 1, 3}}]]];
a[n_] := b[n, 0][[2]];
Table[a[n], {n, 0, 30}] (* Jean-François Alcover, Apr 29 2022, after Alois P. Heinz *)
CROSSREFS
Sequence in context: A353972 A273074 A393716 * A295035 A389154 A295526
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Sep 23 2014
STATUS
approved