Let b(n,0) = n and b(n,k) = 2*b(n,k-1) + 1 for k > 0. Then a(n) = b(n,1) + b(n,2) + ... + b(n,n).

Terms

a(0) =3a(1) =16a(2) =53a(3) =146a(4) =367a(5) =876a(6) =2025a(7) =4582a(8) =10211a(9) =22496a(10) =49117a(11) =106458a(12) =229335a(13) =491476a(14) =1048529a(15) =2228174a(16) =4718539a(17) =9961416a(18) =20971461a(19) =44040130a(20) =92274623a(21) =192937916a(22) =402653113a(23) =838860726a(24) =1744830387a(25) =3623878576a(26) =7516192685a(27) =15569256362a(28) =32212254631a(29) =66571992996