Partial sums of A005248.

Terms

a(0) =2a(1) =5a(2) =12a(3) =30a(4) =77a(5) =200a(6) =522a(7) =1365a(8) =3572a(9) =9350a(10) =24477a(11) =64080a(12) =167762a(13) =439205a(14) =1149852a(15) =3010350a(16) =7881197a(17) =20633240a(18) =54018522a(19) =141422325a(20) =370248452a(21) =969323030a(22) =2537720637a(23) =6643838880a(24) =17393796002a(25) =45537549125a(26) =119218851372a(27) =312119004990a(28) =817138163597