Number of partitions of an n-set without blocks of size 2.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =6a(5) =17a(6) =53a(7) =205a(8) =871a(9) =3876a(10) =18820a(11) =99585a(12) =558847a(13) =3313117a(14) =20825145a(15) =138046940a(16) =959298572a(17) =6974868139a(18) =52972352923a(19) =419104459913