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A316294
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Total number of permutations p of [k] such that n is the maximum of the partial sums of the signed up-down jump sequence of 0,p summed over all k >= 0.
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3
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1, 1, 3, 19, 258, 7406, 442668, 54371100, 13585980916, 6859762797636, 6969135518632452, 14209819222900305044, 58061006907633910998660, 474996314819118381967232244, 7776635831062534849079443379908, 254723669580125156112963535996038036
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OFFSET
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0,3
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COMMENTS
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An up-jump j occurs at position i in p if p_{i} > p_{i-1} and j is the index of p_i in the increasingly sorted list of those elements in {p_{i}, ..., p_{n}} that are larger than p_{i-1}. A down-jump -j occurs at position i in p if p_{i} < p_{i-1} and j is the index of p_i in the decreasingly sorted list of those elements in {p_{i}, ..., p_{n}} that are smaller than p_{i-1}. First index in the lists is 1 here.
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LINKS
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MAPLE
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b:= proc(u, o, c, k) option remember;
`if`(c>k, 0, `if`(u+o=0, 1,
add(b(u-j, o-1+j, c+j, k), j=1..u)+
add(b(u+j-1, o-j, c-j, k), j=1..o)))
end:
a:= n-> add(b(k, 0$2, n)-b(k, 0$2, n-1), k=n..n*(n+1)/2):
seq(a(n), n=0..15);
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MATHEMATICA
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b[u_, o_, c_, k_] := b[u, o, c, k] =
If[c > k, 0, If[u + o == 0, 1,
Sum[b[u - j, o - 1 + j, c + j, k], {j, u}] +
Sum[b[u + j - 1, o - j, c - j, k], {j, o}]]];
a[n_] := Sum[b[k, 0, 0, n] - b[k, 0, 0, n-1], {k, n, n(n+1)/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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