Partial sums of A000048.

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =6a(5) =9a(6) =14a(7) =23a(8) =39a(9) =67a(10) =118a(11) =211a(12) =381a(13) =696a(14) =1281a(15) =2372a(16) =4420a(17) =8275a(18) =15555a(19) =29352a(20) =55566a(21) =105495a(22) =200820a(23) =383181a(24) =732701a(25) =1403789a(26) =2694344a(27) =5179848a(28) =9973338a(29) =19229733