The number of 123-avoiding simple involutions of length n.

Terms

a(0) =1a(1) =2a(2) =0a(3) =0a(4) =2a(5) =3a(6) =2a(7) =5a(8) =10a(9) =17a(10) =22a(11) =44a(12) =68a(13) =127a(14) =184a(15) =356a(16) =530a(17) =1017a(18) =1502a(19) =2906a(20) =4312a(21) =8351a(22) =12388a(23) =24067a(24) =35748a(25) =69577a(26) =103404a(27) =201642a(28) =299882a(29) =585691