a(n) = 2^(2*n - 1) + n.

Terms

a(0) =3a(1) =10a(2) =35a(3) =132a(4) =517a(5) =2054a(6) =8199a(7) =32776a(8) =131081a(9) =524298a(10) =2097163a(11) =8388620a(12) =33554445a(13) =134217742a(14) =536870927a(15) =2147483664a(16) =8589934609a(17) =34359738386a(18) =137438953491a(19) =549755813908