Dirichlet g.f.: Product_{k>=2} (1 + k^(-s))^(5^(k-1)).

Terms

a(0) =1a(1) =5a(2) =25a(3) =135a(4) =625a(5) =3250a(6) =15625a(7) =78760a(8) =390925a(9) =1956250a(10) =9765625a(11) =48847125a(12) =244140625a(13) =1220781250a(14) =6103531250a(15) =30517977755a(16) =152587890625a(17) =762941485875