Partial sums of A005773.

Terms

a(0) =1a(1) =2a(2) =4a(3) =9a(4) =22a(5) =57a(6) =153a(7) =420a(8) =1170a(9) =3293a(10) =9339a(11) =26642a(12) =76363a(13) =219728a(14) =634312a(15) =1836229a(16) =5328346a(17) =15494125a(18) =45137995a(19) =131712826a(20) =384900937a(21) =1126265986a(22) =3299509114a(23) =9676690939a(24) =28407473191a(25) =83470059532a(26) =245465090758a(27) =722406781935