Powers of 4 written backwards and sorted.

Terms

a(0) =1a(1) =4a(2) =46a(3) =61a(4) =652a(5) =4201a(6) =6904a(7) =48361a(8) =63556a(9) =441262a(10) =4034914a(11) =6758401a(12) =46880176a(13) =61277761a(14) =654534862a(15) =4281473701a(16) =6927694924a(17) =48196897171a(18) =63767491786a(19) =449609778472