a(n) = 3*a(n-1) - 2*a(n-2) with a(0)=20 and a(1)=50.

Terms

a(0) =20a(1) =50a(2) =110a(3) =230a(4) =470a(5) =950a(6) =1910a(7) =3830a(8) =7670a(9) =15350a(10) =30710a(11) =61430a(12) =122870a(13) =245750a(14) =491510a(15) =983030a(16) =1966070a(17) =3932150a(18) =7864310a(19) =15728630a(20) =31457270a(21) =62914550a(22) =125829110a(23) =251658230a(24) =503316470a(25) =1006632950a(26) =2013265910a(27) =4026531830a(28) =8053063670a(29) =16106127350