cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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.

Original entry on oeis.org

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

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Author

Jordan Weaver, Apr 16 2020

Keywords

Comments

A length n decorated permutation is a word w = w_1....w_n on the letters {0,...,n} such that the restriction of w to its nonzero entries is an ordinary permutation in one-line notation. Then w avoids 0^m if w contains at most m-1 0's as letters, and w contains 0^m if w contains m 0's among its letters (not necessarily consecutive).

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
		

Crossrefs

Cf. A000142 (1st column), A007526 (right diagonal).
Row sums are A093964.

Programs

  • Mathematica
    Array[Accumulate[#!/Range[0,#-1]!]&,10] (* Paolo Xausa, Jan 08 2024 *)
  • 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