First differences of A000219.

Terms

a(0) =0a(1) =2a(2) =3a(3) =7a(4) =11a(5) =24a(6) =38a(7) =74a(8) =122a(9) =218a(10) =359a(11) =620a(12) =1006a(13) =1682a(14) =2712a(15) =4418a(16) =7037a(17) =11267a(18) =17729a(19) =27948a(20) =43516a(21) =67681a(22) =104308a(23) =160411a(24) =244839a(25) =372712a(26) =563913a(27) =850576a(28) =1276378a(29) =1909351