G.f. A(x) satisfies A(x) = 1 / (1 - x - x * A(x^4)).

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =16a(5) =34a(6) =72a(7) =152a(8) =320a(9) =676a(10) =1428a(11) =3016a(12) =6368a(13) =13448a(14) =28400a(15) =59976a(16) =126656a(17) =267472a(18) =564848a(19) =1192848a(20) =2519056a(21) =5319746a(22) =11234248a(23) =23724504a(24) =50101440a(25) =105804296a(26) =223437672a(27) =471856016a(28) =996466240a(29) =2104338904