A244522 Number of simple involutions of length n.

1, 1, 2, 0, 0, 2, 4, 10, 36, 126, 454, 1744, 6892, 28486, 120962, 531660, 2398248, 11127674, 52888998, 257570104, 1282439216

Offset: 0

Author

Joerg Arndt and Jay Pantone, Jul 21 2014

Keywords

• nonn
• more

Examples

			The a(7) = 10 simple involutions are:
01:  [ 5 1 4 6 2 0 3 ]    (0, 5) (1) (2, 4) (3, 6)
02:  [ 4 1 6 3 0 5 2 ]    (0, 4) (1) (2, 6) (3) (5)
03:  [ 4 6 2 5 0 3 1 ]    (0, 4) (1, 6) (2) (3, 5)
04:  [ 5 3 6 1 4 0 2 ]    (0, 5) (1, 3) (2, 6) (4)
05:  [ 3 1 5 0 6 2 4 ]    (0, 3) (1) (2, 5) (4, 6)
06:  [ 3 5 2 0 6 1 4 ]    (0, 3) (1, 5) (2) (4, 6)
07:  [ 3 6 4 0 2 5 1 ]    (0, 3) (1, 6) (2, 4) (5)
08:  [ 2 5 0 3 6 1 4 ]    (0, 2) (1, 5) (3) (4, 6)
09:  [ 2 5 0 6 4 1 3 ]    (0, 2) (1, 5) (3, 6) (4)
10:  [ 2 4 0 6 1 5 3 ]    (0, 2) (1, 4) (3, 6) (5)
		

Crossrefs

Cf. A000085 (involutions), A111111 (simple permutations).