9^n mod 4^n.

Terms

a(0) =0a(1) =1a(2) =1a(3) =25a(4) =161a(5) =681a(6) =3057a(7) =15225a(8) =55105a(9) =233801a(10) =269201a(11) =3471385a(12) =1882337a(13) =50495465a(14) =186023729a(15) =63600825a(16) =3793632897a(17) =12667859593a(18) =28111390417a(19) =253002513753a(20) =352877275169