Duplicate of A000633.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =1a(6) =1a(7) =3a(8) =7a(9) =18a(10) =42a(11) =109a(12) =269a(13) =691a(14) =1759a(15) =4542a(16) =11733a(17) =30559a(18) =79743a(19) =209136a(20) =549959a(21) =1451178a(22) =3838925a(23) =10182703a(24) =27069940a(25) =72121696a(26) =192527888a(27) =514908269a(28) =1379454526a(29) =3701556642