|
|
A242158
|
|
Number of ascent sequences of length n with exactly five flat steps.
|
|
3
|
|
|
1, 6, 42, 280, 2016, 15372, 125202, 1086624, 10032165, 98284186, 1019176158, 11158475328, 128679348616, 1559469776760, 19819217040840, 263618581334880, 3663049523187915, 53081003095769880, 800881711486787315, 12562640594116484256, 204583362011569856700
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
6,2
|
|
LINKS
|
|
|
FORMULA
|
a(n) ~ Pi^(15/2)/(25920*sqrt(3)*exp(Pi^2/12)) * (6/Pi^2)^n * n! * sqrt(n). - Vaclav Kotesovec, Aug 27 2014
|
|
MATHEMATICA
|
b[n_, i_, t_] := b[n, i, t] = If[n == 0, 1, Expand[Sum[ If[j == i, x, 1]*b[n - 1, j, t + If[j > i, 1, 0]], {j, 0, t + 1}]]]; a[n_] := Coefficient[b[n, -1, -1], x, 5]; Table[a[n], {n, 6, 30}] (* Jean-François Alcover, Feb 10 2015, after A242153 *)
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|