A121079 a(n) = Sum_{i=0..n} C(n,i)^2*i!*4^i + 2^n*n!.
2, 7, 57, 757, 13889, 322021, 8962225, 289928549, 10666353409, 439225736005, 19999574572721, 997265831223685, 54028099173536449, 3159178743189436709, 198259676112757095985, 13289233274778582230821, 947420482287986880154625, 71574264415491967142194309
Offset: 0
Keywords
Links
- Michael De Vlieger, Table of n, a(n) for n = 0..363
- Joël Gay, Representation of Monoids and Lattice Structures in the Combinatorics of Weyl Groups, Doctoral Thesis, Discrete Mathematics [cs.DM], Université Paris-Saclay, 2018.
- Z. Li, Z. Li and Y. Cao, Enumeration of symplectic and orthogonal injective partial transformations, Discrete Math., 306 (2006), 1781-1787.
Programs
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Mathematica
Array[Sum[Binomial[#, i]^2*i!*4^i, {i, 0, #}] + 2^#*#! &, 18, 0] (* Michael De Vlieger, Nov 28 2018 *) -
PARI
a(n) = 2^n*n! + sum(i=0, n, binomial(n,i)^2*i!*4^i); \\ Michel Marcus, May 31 2018