|
| |
|
|
A095817
|
|
Number of permutations of 1..n with no four elements in correct or reverse order.
|
|
2
| |
|
|
1, 2, 6, 22, 114, 692, 4884, 39318, 355490, 3567292, 39345804, 473148014, 6161310442, 86376341412, 1297099489668, 20772929663254, 353415786538434, 6365693021157116, 121016486728717740
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 1,2
|
|
|
COMMENTS
| For no n do either of the subsequences n(n+1)(n+2)(n+3) or (n+3)(n+2)(n+1)n occur in any permutation.
|
|
|
LINKS
| 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, A095816, A095818.
Sequence in context: A129535 A014371 A111280 * A101042 A171339 A032266
Adjacent sequences: A095814 A095815 A095816 * A095818 A095819 A095820
|
|
|
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
|
| |
|
|
