a(n) = 57*2^(n-1) - 38 (n >= 1).

Terms

a(0) =19a(1) =76a(2) =190a(3) =418a(4) =874a(5) =1786a(6) =3610a(7) =7258a(8) =14554a(9) =29146a(10) =58330a(11) =116698a(12) =233434a(13) =466906a(14) =933850a(15) =1867738a(16) =3735514a(17) =7471066a(18) =14942170a(19) =29884378a(20) =59768794a(21) =119537626a(22) =239075290a(23) =478150618a(24) =956301274a(25) =1912602586a(26) =3825205210a(27) =7650410458a(28) =15300820954a(29) =30601641946