a(0)=2; for n > 0, a(n) = 2^(2*n-1) + 2^n + 1.

Terms

a(0) =2a(1) =5a(2) =13a(3) =41a(4) =145a(5) =545a(6) =2113a(7) =8321a(8) =33025a(9) =131585a(10) =525313a(11) =2099201a(12) =8392705a(13) =33562625a(14) =134234113a(15) =536903681a(16) =2147549185a(17) =8590065665a(18) =34360000513a(19) =137439477761a(20) =549756862465