a(n) = 420*2^n - 222.

Terms

a(0) =198a(1) =618a(2) =1458a(3) =3138a(4) =6498a(5) =13218a(6) =26658a(7) =53538a(8) =107298a(9) =214818a(10) =429858a(11) =859938a(12) =1720098a(13) =3440418a(14) =6881058a(15) =13762338a(16) =27524898a(17) =55050018a(18) =110100258a(19) =220200738a(20) =440401698a(21) =880803618a(22) =1761607458a(23) =3523215138a(24) =7046430498a(25) =14092861218a(26) =28185722658a(27) =56371445538a(28) =112742891298