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A121080
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a(n) = Sum_{i=0..n} C(n,i)^2*i!*4^i + (1-2^n)*2^(n-1)*n!.
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2
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1, 4, 37, 541, 10625, 258661, 7464625, 248318309, 9339986689, 391569431365, 18095180332721, 913513359466885, 50008961524486849, 2950209091316054309, 186558089772409191985, 12587159519294553302821, 902488447534988078746625, 68518909362619336345906309
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OFFSET
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0,2
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LINKS
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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.
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MATHEMATICA
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Array[Sum[Binomial[#, i]^2*i!*4^i, {i, 0, #}] + (1 - 2^#)*2^(# - 1)*#! &, 18, 0] (* Michael De Vlieger, Nov 28 2018 *)
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PROG
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(PARI) a(n) = (1-2^n)*2^(n-1)*n! + sum(i=0, n, binomial(n, i)^2*i!*4^i); \\ Michel Marcus, May 31 2018
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CROSSREFS
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Cf. A102773, A121079.
Sequence in context: A277638 A352237 A349714 * A001518 A185082 A259822
Adjacent sequences: A121077 A121078 A121079 * A121081 A121082 A121083
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane, Aug 11 2006
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STATUS
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approved
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