a(n) = 10*4^n.

Terms

a(0) =10a(1) =40a(2) =160a(3) =640a(4) =2560a(5) =10240a(6) =40960a(7) =163840a(8) =655360a(9) =2621440a(10) =10485760a(11) =41943040a(12) =167772160a(13) =671088640a(14) =2684354560a(15) =10737418240a(16) =42949672960a(17) =171798691840a(18) =687194767360