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A138619
Number of permutations of length n which are contained in a pin sequence.
0
1, 2, 6, 24, 120, 664, 3596, 19004, 99596, 521420, 2731292, 14313052, 75016940, 393181820, 2060736460, 10800601788, 56607287052, 296685718140, 1554966533836, 8149773122044, 42713977098636, 223869280280316
OFFSET
1,2
LINKS
F. Bassino, M. Bouvel, and D. Rossin, Enumeration of Pin-Permutations, The Electronic Journal of Combinatorics, Vol. 18, No. 1 (2011), P57. [Vincent Vatter, Sep 15 2009]
R. Brignall, N. Ruskuc and V. Vatter, Simple permutations: decidability and unavoidable substructures, Theoretical Computer Science 391 (2008), 150-163.
FORMULA
G.f.: (1-7*x+13*x^2-17*x^3+2*x^4-8*x^5+12*x^6+12*x^7-8*x^8) / (1-8*x+19*x^2-26*x^3+14*x^4-12*x^5-8*x^6+20*x^7-8*x^8). See Bassino, Bouvel, and Rossin. [Vincent Vatter, Sep 15 2009]
EXAMPLE
a(5)=120 because all permutations of length 5 can be embedded into pin sequences.
CROSSREFS
Sequence in context: A152336 A152343 A177529 * A372545 A189841 A189256
KEYWORD
nonn
AUTHOR
Vincent Vatter, May 14 2008
EXTENSIONS
Extended (using g.f.) by Vincent Vatter, Sep 15 2009
STATUS
approved