Partial sums of A004080.

Terms

a(0) =1a(1) =5a(2) =16a(3) =47a(4) =130a(5) =357a(6) =973a(7) =2647a(8) =7197a(9) =19564a(10) =53181a(11) =144561a(12) =392958a(13) =1068172a(14) =2903593a(15) =7892784a(16) =21454811a(17) =58320223a(18) =158530804a(19) =430931404a(20) =1171393005a(21) =3184176320a(22) =8655488630a(23) =23528057461a(24) =63955891057a(25) =173850136486a(26) =472573666887