A317140 Number of permutations of [2n+1] with exactly n increasing runs of length two.

1, 4, 43, 906, 31493, 1629248, 117248463, 11190963430, 1367267690953, 208031951035452, 38563334673062963, 8554779137299629314, 2237467931691025532493, 681305299577272105281016, 238929711424864185326131543, 95603626135129502838914478558

Offset: 0

Author

Alois P. Heinz, Jul 22 2018

Keywords

• nonn

Examples

			a(1) = 4: 132, 213, 231, 312.
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 0..242

Crossrefs

Bisection (odd part) of A317139.

Cf. A097592.

Formula

a(n) = A317139(2n+1) = A097592(2n+1,n).

a(n) + n == 1 (mod 2).