a(n) = 836*2^n - 676.

Terms

a(0) =160a(1) =996a(2) =2668a(3) =6012a(4) =12700a(5) =26076a(6) =52828a(7) =106332a(8) =213340a(9) =427356a(10) =855388a(11) =1711452a(12) =3423580a(13) =6847836a(14) =13696348a(15) =27393372a(16) =54787420a(17) =109575516a(18) =219151708a(19) =438304092a(20) =876608860a(21) =1753218396a(22) =3506437468a(23) =7012875612a(24) =14025751900a(25) =28051504476a(26) =56103009628a(27) =112206019932a(28) =224412040540a(29) =448824081756