|
| |
|
|
A095816
|
|
Number of permutations of 1..n with no three elements in correct or reverse order.
|
|
8
|
|
|
|
1, 1, 2, 4, 18, 92, 570, 4082, 33292, 304490, 3086890, 34357812, 416526730, 5463479106, 77094352076, 1164544912938, 18749754351338, 320544941916628, 5799226664694602, 110695180631374114, 2223242026407894732
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
0,3
|
|
|
COMMENTS
|
Counts permutations with the property that no subsequence i(i+1)(i+2) or (i+2)(i+1)i occurs.
|
|
|
LINKS
|
Table of n, a(n) for n=0..20.
Jackson, D. M. and Read, R. C., A note on permutations without runs of given length, Aequationes Math. 17 (1978), no. 2-3, 336-343.
|
|
|
FORMULA
|
G.f. for number of permutations of 1..n with no m elements in correct or reverse order is Sum(n!*((2*x^m-x^(m+1)-x)/(x^m-1))^n,n=0..infinity). - Ivana Jovovic ( ivana121(AT)EUnet.yu ), Nov 11 2007
|
|
|
CROSSREFS
|
Cf. A002464, A095817, A095818.
Cf. A165963, A165964, A078628. [From Isaac Lambert, Oct 07 2009]
Sequence in context: A014448 A075836 A120664 * A020101 A099938 A135069
Adjacent sequences: A095813 A095814 A095815 * A095817 A095818 A095819
|
|
|
KEYWORD
|
nonn
|
|
|
AUTHOR
|
Jonas Wallgren (jonwa(AT)ida.liu.se), Jun 08 2004
|
|
|
EXTENSIONS
|
More terms from Ivana Jovovic ( ivana121(AT)EUnet.yu ), Nov 11 2007
a(0)=1 prepended by Max Alekseyev, Jun 14 2011
|
|
|
STATUS
|
approved
|
| |
|
|
