OFFSET
0,4
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..250
EXAMPLE
a(0) = 1: ().
a(1) = 1: 1.
a(2) = 1: 21.
a(3) = 4: 132, 213, 231, 321.
a(4) = 8: 1324, 2413, 2431, 3241, 4132, 4213, 4231, 4321.
a(5) = 54: 13245, 13254, 13524, ..., 54213, 54231, 54321.
a(6) = 162: 132465, 132546, 132645, ..., 654213, 654231, 654321.
MAPLE
a:= n-> ceil(n/2)!*ceil(n/2)^floor(n/2):
seq(a(n), n=0..30);
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Nov 11 2013
STATUS
approved