a(n) = 123*2^n - 99.

Terms

a(0) =24a(1) =147a(2) =393a(3) =885a(4) =1869a(5) =3837a(6) =7773a(7) =15645a(8) =31389a(9) =62877a(10) =125853a(11) =251805a(12) =503709a(13) =1007517a(14) =2015133a(15) =4030365a(16) =8060829a(17) =16121757a(18) =32243613a(19) =64487325a(20) =128974749a(21) =257949597a(22) =515899293a(23) =1031798685a(24) =2063597469a(25) =4127195037a(26) =8254390173a(27) =16508780445a(28) =33017560989a(29) =66035122077