|
| |
|
|
A145846
|
|
Number of permutations of length 2n which are invariant under the reverse-complement map and have no decreasing subsequences of length 6.
|
|
0
| |
|
|
1, 2, 8, 47, 357, 3270, 34515, 406460, 5215829, 71677058, 1041363040, 15841778155, 250494079945, 4093630537014
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 0,2
|
|
|
FORMULA
| a(n) = sum(j, 0, n, C(n,j)^2 * A000108(n-j) * A005802(j)),
where C(n,j) = n!/(j!(n-j)!)
|
|
|
MATHEMATICA
| Table[Sum[ Binomial[n, j]^2*((1/(n - j + 1))* Binomial[2*(n - j), n - j]/((j + 1)^2*(j + 2)))* Sum[Binomial[2*i, i]*Binomial[j + 1, i + 1]* Binomial[j + 2, i + 1], {i, 0, j}], {j, 0, n}], {n, 0, 20}]
|
|
|
CROSSREFS
| Sequence in context: A096656 A102009 A135904 * A009566 A199136 A181413
Adjacent sequences: A145843 A145844 A145845 * A145847 A145848 A145849
|
|
|
KEYWORD
| nonn
|
|
|
AUTHOR
| Eric Egge (eegge(AT)carleton.edu), Oct 21 2008
|
| |
|
|
