Numbers with digits 2 and 4 only.

Terms

a(0) =2a(1) =4a(2) =22a(3) =24a(4) =42a(5) =44a(6) =222a(7) =224a(8) =242a(9) =244a(10) =422a(11) =424a(12) =442a(13) =444a(14) =2222a(15) =2224a(16) =2242a(17) =2244a(18) =2422a(19) =2424a(20) =2442a(21) =2444a(22) =4222a(23) =4224a(24) =4242a(25) =4244a(26) =4422a(27) =4424a(28) =4442a(29) =4444