a(n) = 30*2^n + 12.

Terms

a(0) =42a(1) =72a(2) =132a(3) =252a(4) =492a(5) =972a(6) =1932a(7) =3852a(8) =7692a(9) =15372a(10) =30732a(11) =61452a(12) =122892a(13) =245772a(14) =491532a(15) =983052a(16) =1966092a(17) =3932172a(18) =7864332a(19) =15728652a(20) =31457292a(21) =62914572a(22) =125829132a(23) =251658252a(24) =503316492a(25) =1006632972a(26) =2013265932a(27) =4026531852a(28) =8053063692a(29) =16106127372