a(n) = a(n-1)*a(n-3)+1 with a(0)=a(1)=a(2)=0.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =1a(5) =1a(6) =2a(7) =3a(8) =4a(9) =9a(10) =28a(11) =113a(12) =1018a(13) =28505a(14) =3221066a(15) =3279045189