Partial sums of A003418.

Terms

a(0) =1a(1) =2a(2) =4a(3) =10a(4) =22a(5) =82a(6) =142a(7) =562a(8) =1402a(9) =3922a(10) =6442a(11) =34162a(12) =61882a(13) =422242a(14) =782602a(15) =1142962a(16) =1863682a(17) =14115922a(18) =26368162a(19) =259160722a(20) =491953282a(21) =724745842a(22) =957538402a(23) =6311767282a(24) =11665996162a(25) =38437140562a(26) =65208284962a(27) =145521718162a(28) =225835151362