OFFSET
0,3
FORMULA
a(n) = A259784(2n,n).
EXAMPLE
a(0) = 1: (the empty permutation).
a(1) = 1: 21.
a(2) = 3: 2413, 3142, 3412.
a(3) = 44: 214563, 215643, 216345, ..., 451623, 452163, 456123.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Alois P. Heinz, Jul 05 2015
STATUS
approved