a(n) = 10^n mod 4^n.

Terms

a(0) =0a(1) =2a(2) =4a(3) =40a(4) =16a(5) =672a(6) =576a(7) =5760a(8) =57600a(9) =182784a(10) =779264a(11) =3598336a(12) =10817536a(13) =41066496a(14) =8011776a(15) =616988672a(16) =1874919424a(17) =1569325056a(18) =15693250560a(19) =19493552128a(20) =194935521280