A000434 Number of permutations of [n] in which the longest increasing run has length 4. (Formerly M4556 N1938)

0, 0, 0, 1, 8, 67, 602, 5811, 60875, 690729, 8457285, 111323149, 1569068565, 23592426102, 377105857043, 6387313185576, 114303481217657, 2155348564847332, 42719058006864690, 887953677898186108, 19316200230609433690, 438920223893512987430

Offset

1,5

References

F. N. David, M. G. Kendall and D. E. Barton, Symmetric Function and Allied Tables, Cambridge, 1966, p. 261. (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).

Links

Alois P. Heinz, Table of n, a(n) for n = 1..450 (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

Example

a(5)=8 because we have (1235)4, (1245)3, (1345)2, (2345)1, 5(1234), 4(1235), 3(1245) and 2(1345), where the parentheses surround increasing runs of length 4.

Mathematica

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, 4];
Array[a, 30] (* Jean-François Alcover, Jul 19 2018, after Alois P. Heinz *)

Crossrefs

Column 4 of A008304. Other columns: A000303, A000402, A000456, A000467.

Cf. A001250, A001251, A001252, A001253, A010026, A211318.

Sequence in context: A370028 A152055 A363309 * A304073 A250258 A192091

Adjacent sequences: A000431 A000432 A000433 * A000435 A000436 A000437

Keyword

nonn

Author

N. J. A. Sloane

Extensions

Better description from Emeric Deutsch, May 08 2004

Terms a(16)-a(18) corrected and further terms added by Max Alekseyev, May 20 2012

Status

approved