a(n) = 0^n + 5^n - 1.

Terms

a(0) =1a(1) =4a(2) =24a(3) =124a(4) =624a(5) =3124a(6) =15624a(7) =78124a(8) =390624a(9) =1953124a(10) =9765624a(11) =48828124a(12) =244140624a(13) =1220703124a(14) =6103515624a(15) =30517578124a(16) =152587890624a(17) =762939453124