a(n) = Sum_{k=1..n} (binomial(n, k) * 4^k) (mod 5^k).

Terms

a(0) =4a(1) =19a(2) =89a(3) =284a(4) =1079a(5) =7254a(6) =32524a(7) =125419a(8) =505889a(9) =1947259a(10) =6994834a(11) =20189904a(12) =328654224a(13) =1289356494a(14) =6126904264a(15) =24165821664a(16) =120780761134a(17) =450207093504