login
This site is supported by donations to The OEIS Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A093345 a(n) = n! * {1 + Sum[i=1..n, 1/i*Sum(j=0..i-1, 1/j!)]}. 2
1, 2, 6, 23, 108, 605, 3956, 29649, 250892, 2367629, 24662700, 281153801, 3482350724, 46572620757, 668943488084, 10271127486065, 167892667249116, 2911049382788189, 53365747562592092, 1031352659792534169 (list; graph; refs; listen; history; text; internal format)
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 2-letter signed patterns, arXiv:math/0207204 [math.CO], 2002.

FORMULA

E.g.f.: (exp(1)*(Ei(1, 1-x)-Ei(1, 1))+1)/(1-x). a(n) = n!*(1+Sum(A000522(i-1)/i!, i =1..n)). - Vladeta Jovovic, Apr 27 2004

Conjecture: a(n) -2*n*a(n-1) +(n^2-2)*a(n-2) -(n-2)^2*a(n-3)=0. - R. J. Mathar, May 30 2014

MATHEMATICA

a[n_] := n! (1+Sum[1/i Sum[1/j!, {j, 0, i-1}], {i, 1, n}])

Table[a[n], {n, 0, 19}] (* Jean-Fran├žois Alcover, Oct 05 2018 *)

PROG

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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 8 18:37 EST 2019. Contains 329865 sequences. (Running on oeis4.)