Partial sums of A003407 (starting at n=1).

Terms

a(0) =1a(1) =3a(2) =7a(3) =17a(4) =37a(5) =85a(6) =189a(7) =471a(8) =967a(9) =2033a(10) =4493a(11) =10621a(12) =23461a(13) =52841a(14) =127745a(15) =340473a(16) =708489a(17) =1367785a(18) =2738841a(19) =5675977a(20) =12313209a(21) =27929825a(22) =66361381a(23) =162909213a(24) =361319381a(25) =780460693a(26) =1722272781a(27) =3904263759a(28) =9528920767a(29) =24294326763