Number of compositions of n with the multiplicity of the first part even.

Terms

a(0) =0a(1) =1a(2) =0a(3) =4a(4) =4a(5) =14a(6) =20a(7) =56a(8) =98a(9) =224a(10) =420a(11) =902a(12) =1764a(13) =3664a(14) =7258a(15) =14824a(16) =29596a(17) =59942a(18) =120012a(19) =241944a(20) =484946a(21) =975216a(22) =1955244a(23) =3926078a(24) =7870980a(25) =15790272a(26) =31650090a(27) =63456208a(28) =127162580a(29) =254845446