a(0) = 1; a(n) = Sum_{k=0..floor((n-1)/7)} a(7*k) * a(n-1-7*k).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =1a(6) =1a(7) =1a(8) =2a(9) =3a(10) =4a(11) =5a(12) =6a(13) =7a(14) =8a(15) =17a(16) =27a(17) =38a(18) =50a(19) =63a(20) =77a(21) =92a(22) =200a(23) =325a(24) =468a(25) =630a(26) =812a(27) =1015a(28) =1240a(29) =2728