A334156 Triangle read by rows: T(n,m) is the number of length n decorated permutations avoiding the word 0^m = 0...0 of m 0's, where 1 <= m <= n.
1, 2, 4, 6, 12, 15, 24, 48, 60, 64, 120, 240, 300, 320, 325, 720, 1440, 1800, 1920, 1950, 1956, 5040, 10080, 12600, 13440, 13650, 13692, 13699, 40320, 80640, 100800, 107520, 109200, 109536, 109592, 109600, 362880, 725760, 907200, 967680, 982800, 985824, 986328, 986400, 986409
Offset: 1
Examples
For (n,m) = (3,2), the T(3,2) = 12 length 3 decorated permutations avoiding 0^2 = 00 are 012, 102, 120, 021, 201, 210, 123, 132, 213, 231, 312, and 321. Triangle begins: 1 2, 4 6, 12, 15 24, 48, 60, 64 120, 240, 300, 320, 325
Links
- Andrew Howroyd, Table of n, a(n) for n = 1..1275 (rows 1..50)
- S. Corteel, Crossings and alignments of permutations, Adv. Appl. Math 38 (2007) 149-163.
- A. Postnikov, Total positivity, Grassmannians, and networks, arXiv:math/0609764 [math.CO], 2006.
Programs
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Mathematica
Array[Accumulate[#!/Range[0,#-1]!]&,10] (* Paolo Xausa, Jan 08 2024 *)
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PARI
T(n,m)={sum(j=0, m-1, n!/j!)} \\ Andrew Howroyd, May 11 2020
Formula
T(n,m) = Sum_{j=0..m-1} n!/j!.
Extensions
Terms a(37) and beyond from Andrew Howroyd, Jan 07 2024
Comments