a(n) = 5^n mod 4^n.

Terms

a(0) =0a(1) =1a(2) =9a(3) =61a(4) =113a(5) =53a(6) =3337a(7) =12589a(8) =62945a(9) =118117a(10) =328441a(11) =2690781a(12) =9259601a(13) =12743573a(14) =197935593a(15) =452807053a(16) =2264035265a(17) =7025209029a(18) =35126045145a(19) =106910748989a(20) =809431651889