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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A124419 Number of partitions of the set {1,2,...n} having no blocks that contain both odd and even entries. 14
1, 1, 1, 2, 4, 10, 25, 75, 225, 780, 2704, 10556, 41209, 178031, 769129, 3630780, 17139600, 87548580, 447195609, 2452523325, 13450200625, 78697155750, 460457244900, 2859220516290, 17754399678409, 116482516809889, 764214897046969, 5277304280371714 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

Column 0 of A124418.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..500

A. Dzhumadil’daev and D. Yeliussizov, Path decompositions of digraphs and their applications to Weyl algebra, arXiv preprint arXiv:1408.6764v1, 2014. [Version 1 contained many references to the OEIS, which were removed in Version 2. - N. J. A. Sloane, Mar 28 2015]

Askar Dzhumadil’daev and Damir Yeliussizov, Walks, partitions, and normal ordering, Electronic Journal of Combinatorics, 22(4) (2015), #P4.10.

FORMULA

a(n) = Q[n](1,1,0), where the polynomials Q[n]=Q[n](t,s,x) are defined by Q[0]=1; Q[n]=t*dQ[n-1]/dt + x*dQ[n-1]/ds + x*dQ[n-1]/dx + t*Q[n-1] if n is odd and Q[n]=x*dQ[n-1]/dt + s*dQ[n-1]/ds + x*dQ[n-1]/dx + s*Q[n-1] if n is even.

a(n) = A000110(floor(n/2)) * A000110(ceiling(n/2)). - Alois P. Heinz, Oct 23 2013

EXAMPLE

a(4) = 4 because we have 13|24, 1|24|3, 13|2|4 and 1|2|3|4.

MAPLE

Q[0]:=1: for n from 1 to 30 do if n mod 2 = 1 then Q[n]:=expand(t*diff(Q[n-1], t)+x*diff(Q[n-1], s)+x*diff(Q[n-1], x)+t*Q[n-1]) else Q[n]:=expand(x*diff(Q[n-1], t)+s*diff(Q[n-1], s)+x*diff(Q[n-1], x)+s*Q[n-1]) fi od: for n from 0 to 30 do Q[n]:=Q[n] od: seq(subs({t=1, s=1, x=0}, Q[n]), n=0..30);

# second Maple program:

with(combinat):

a:= n-> bell(floor(n/2))*bell(ceil(n/2)):

seq(a(n), n=0..30);  # Alois P. Heinz, Oct 23 2013

MATHEMATICA

a[n_] := BellB[Floor[n/2]]*BellB[Ceiling[n/2]]; Table[a[n], {n, 0, 30}] (* Jean-François Alcover, May 20 2015, after Alois P. Heinz *)

CROSSREFS

Cf. A000110, A124418, A124420, A124421, A124422, A124423, A274310.

Column k=2 of A275069.

Sequence in context: A206289 A148094 A148095 * A148096 A006901 A123422

Adjacent sequences:  A124416 A124417 A124418 * A124420 A124421 A124422

KEYWORD

nonn

AUTHOR

Emeric Deutsch, Oct 31 2006

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified July 22 03:22 EDT 2017. Contains 289648 sequences.