|
|
A054394
|
|
Number of permutations with certain forbidden subsequences.
|
|
2
|
|
|
1, 1, 2, 5, 14, 42, 132, 429, 1429, 4847, 16660, 57820, 202086, 709928, 2503266, 8850681, 31355020, 111242127, 395091069, 1404332528, 4994581900, 17771328588, 63253477326, 225194224134, 801884971816, 2855809269782, 10171707099565
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,3
|
|
LINKS
|
|
|
FORMULA
|
|
|
MATHEMATICA
|
a[0] = 1; a[n_] := Module[{M}, M = Table[If[j < i || i == j && i <= 6 || j == i+1, 1, 0], {i, 1, n}, {j, 1, n}]; MatrixPower[M, n][[1, 1]]];
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|