Number of (3412,2341)-, (3412,4123)- and (3412,52341)-avoiding involutions in S_n.

Terms

a(0) =1a(1) =2a(2) =4a(3) =9a(4) =20a(5) =45a(6) =100a(7) =222a(8) =491a(9) =1086a(10) =2401a(11) =5310a(12) =11744a(13) =25977a(14) =57460a(15) =127101a(16) =281144a(17) =621882a(18) =1375579a(19) =3042726a(20) =6730385a(21) =14887338a(22) =32930188a(23) =72840249a(24) =161119700a(25) =356390301a(26) =788321020a(27) =1743734406a(28) =3857070395a(29) =8531684622