a(n) = 1 + Sum_{k=0..n-4} binomial(n-3,k) * a(k).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =4a(6) =8a(7) =16a(8) =37a(9) =97a(10) =275a(11) =810a(12) =2468a(13) =7840a(14) =26182a(15) =92047a(16) =339029a(17) =1299185a(18) =5152244a(19) =21091816a(20) =89087652a(21) =388318264a(22) =1746324563a(23) =8094422821a(24) =38608318847a(25) =189179752492a(26) =950930369320