G.f. A(x) satisfies A(x) = 1 / (1 - x - x * (1 + x + x^2 + x^3) * A(x^4)).

Terms

a(0) =1a(1) =2a(2) =5a(3) =13a(4) =34a(5) =90a(6) =238a(7) =629a(8) =1662a(9) =4394a(10) =11616a(11) =30707a(12) =81173a(13) =214584a(14) =567259a(15) =1499563a(16) =3964128a(17) =10479273a(18) =27702219a(19) =73231500a(20) =193589270a(21) =511758023a(22) =1352844978a(23) =3576279113a(24) =9453982143a(25) =24991835308a(26) =66066533905a(27) =174648514118a(28) =461687660561