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A244522
Number of simple involutions of length n.
1
1, 1, 2, 0, 0, 2, 4, 10, 36, 126, 454, 1744, 6892, 28486, 120962, 531660, 2398248, 11127674, 52888998, 257570104, 1282439216
OFFSET
0,3
EXAMPLE
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).
Sequence in context: A127862 A342223 A223142 * A292945 A024690 A200728
KEYWORD
nonn,more
AUTHOR
Joerg Arndt and Jay Pantone, Jul 21 2014
STATUS
approved