Powers of 2 written in base 4.

Terms

a(0) =1a(1) =2a(2) =10a(3) =20a(4) =100a(5) =200a(6) =1000a(7) =2000a(8) =10000a(9) =20000a(10) =100000a(11) =200000a(12) =1000000a(13) =2000000a(14) =10000000a(15) =20000000a(16) =100000000a(17) =200000000a(18) =1000000000a(19) =2000000000a(20) =10000000000a(21) =20000000000a(22) =100000000000a(23) =200000000000a(24) =1000000000000