|
Search: id:A033305
|
|
|
| A033305 |
|
Number of permutations (p1,...,pn) such that 1<=|pk-k|<=2 for all k. |
|
+0
1
|
|
| 1, 0, 1, 2, 4, 6, 13, 24, 45, 84, 160, 300, 565, 1064, 2005, 3774, 7108, 13386, 25209, 47472, 89401, 168360, 317056, 597080, 1124425, 2117520, 3987721, 7509690, 14142276, 26632782, 50154949, 94451976, 177872293
(list; graph; listen)
|
|
|
OFFSET
|
0,4
|
|
|
REFERENCES
|
Lehmer, D. H.; Permutations with strongly restricted displacements. Combinatorial theory and its applications, II (Proc. Colloq., Balatonfured, 1969), pp. 755-770. North-Holland, Amsterdam, 1970.
R. P. Stanley, Enumerative Combinatorics I, p. 252, Example 4.7.16.
|
|
FORMULA
|
G.f.: (1-x)/(1-x-x^2-x^3-x^4+x^5).
a(n) = a(n-1) + a(n-2) + a(n-3) + a(n-4) - a(n-5)
|
|
CROSSREFS
|
Sequence in context: A058598 A087549 A109078 this_sequence A105543 A027712 A138307
Adjacent sequences: A033302 A033303 A033304 this_sequence A033306 A033307 A033308
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
N. J. A. Sloane (njas(AT)research.att.com).
|
|
EXTENSIONS
|
New description from Max Alekseyev (maxale(AT)gmail.com), Jul 09 2006
|
|
|
Search completed in 0.002 seconds
|
