

A093345


a(n) = n! * {1 + Sum[i=1..n, 1/i*Sum(j=0..i1, 1/j!)]}.


2



1, 2, 6, 23, 108, 605, 3956, 29649, 250892, 2367629, 24662700, 281153801, 3482350724, 46572620757, 668943488084, 10271127486065, 167892667249116, 2911049382788189, 53365747562592092, 1031352659792534169
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OFFSET

0,2


COMMENTS

Number of {12,2*1}avoiding signed permutations in the hyperoctahedral group B_n.


LINKS

Table of n, a(n) for n=0..19.
D. Daly and L. Pudwell, Pattern avoidance in rook monoids, 2013.  From N. J. A. Sloane, Feb 03 2013
T. Mansour and J. West, Avoiding 2letter signed patterns, arXiv:math/0207204 [math.CO], 2002.


FORMULA

E.g.f.: (exp(1)*(Ei(1, 1x)Ei(1, 1))+1)/(1x). a(n) = n!*(1+Sum(A000522(i1)/i!, i =1..n)).  Vladeta Jovovic, Apr 27 2004
Conjecture: a(n) 2*n*a(n1) +(n^22)*a(n2) (n2)^2*a(n3)=0.  R. J. Mathar, May 30 2014


MATHEMATICA

a[n_] := n! (1+Sum[1/i Sum[1/j!, {j, 0, i1}], {i, 1, n}])
Table[a[n], {n, 0, 19}] (* JeanFrançois Alcover, Oct 05 2018 *)


PROG

(PARI) a(n)=n!+n!*sum(i=1, n, 1/i*sum(j=0, i1, 1/j!))


CROSSREFS

Cf. A000774.
Cf. A000522, A093344.
Contribution from Johannes W. Meijer, Oct 16 2009: (Start)
Equals row sums of A165675.
(End)
Sequence in context: A071076 A297196 A112501 * A289681 A002136 A328441
Adjacent sequences: A093342 A093343 A093344 * A093346 A093347 A093348


KEYWORD

nonn


AUTHOR

Ralf Stephan, Apr 26 2004


STATUS

approved



