A244522 - OEIS

%I #8 Jul 22 2014 02:38:21

%S 1,1,2,0,0,2,4,10,36,126,454,1744,6892,28486,120962,531660,2398248,

%T 11127674,52888998,257570104,1282439216

%N Number of simple involutions of length n.

%e The a(7) = 10 simple involutions are:

%e 01:  [ 5 1 4 6 2 0 3 ]    (0, 5) (1) (2, 4) (3, 6)

%e 02:  [ 4 1 6 3 0 5 2 ]    (0, 4) (1) (2, 6) (3) (5)

%e 03:  [ 4 6 2 5 0 3 1 ]    (0, 4) (1, 6) (2) (3, 5)

%e 04:  [ 5 3 6 1 4 0 2 ]    (0, 5) (1, 3) (2, 6) (4)

%e 05:  [ 3 1 5 0 6 2 4 ]    (0, 3) (1) (2, 5) (4, 6)

%e 06:  [ 3 5 2 0 6 1 4 ]    (0, 3) (1, 5) (2) (4, 6)

%e 07:  [ 3 6 4 0 2 5 1 ]    (0, 3) (1, 6) (2, 4) (5)

%e 08:  [ 2 5 0 3 6 1 4 ]    (0, 2) (1, 5) (3) (4, 6)

%e 09:  [ 2 5 0 6 4 1 3 ]    (0, 2) (1, 5) (3, 6) (4)

%e 10:  [ 2 4 0 6 1 5 3 ]    (0, 2) (1, 4) (3, 6) (5)

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

%K nonn,more

%O 0,3

%A _Joerg Arndt_ and _Jay Pantone_, Jul 21 2014