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A000402
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Number of permutations of [n] in which the longest increasing run has length 3.
(Formerly M4239 N1771)
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6
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0, 0, 1, 6, 41, 293, 2309, 19975, 189524, 1960041, 21993884, 266361634, 3465832370, 48245601976, 715756932697, 11277786883720, 188135296651083, 3313338641692957, 61444453534759589, 1196988740015236617, 24442368179977776766, 522124104504306695929
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OFFSET
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1,4
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REFERENCES
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F. N. David, M. G. Kendall and D. E. Barton, Symmetric Function and Allied Tables, Cambridge, 1966, p. 261, Table 7.4.1. (Values for n>=16 are incorrect.)
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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Alois P. Heinz, Table of n, a(n) for n = 1..452 (first 100 terms from Max Alekseyev)
Max A. Alekseyev, On the number of permutations with bounded runs length, arXiv preprint arXiv:1205.4581 [math.CO], 2012-2013. - From N. J. A. Sloane, Oct 23 2012
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EXAMPLE
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a(4)=6 because we have (124)3, (134)2, (234)1, 4(123), 3(124) and 2(134), where the parentheses surround increasing runs of length 3.
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MATHEMATICA
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b[u_, o_, t_, k_] := b[u, o, t, k] = If[t == k, (u + o)!, If[Max[t, u] + o < k, 0, Sum[b[u + j - 1, o - j, t + 1, k], {j, 1, o}] + Sum[b[u - j, o + j - 1, 1, k], {j, 1, u}]]];
T[n_, k_] := b[0, n, 0, k] - b[0, n, 0, k + 1];
a[n_] := T[n, 3];
Array[a, 30] (* Jean-François Alcover, Jul 19 2018, after Alois P. Heinz *)
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CROSSREFS
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Column 3 of A008304. Other columns: A000303, A000434, A000456, A000467.
Cf. A001250, A001251, A001252, A001253, A010026, A211318.
Sequence in context: A196954 A122371 A083067 * A186654 A152107 A143023
Adjacent sequences: A000399 A000400 A000401 * A000403 A000404 A000405
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane
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EXTENSIONS
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Better description from Emeric Deutsch, May 08 2004
Terms a(16), a(17) are corrected and further terms added by Max Alekseyev, May 20 2012
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STATUS
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approved
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