a(n) = denominators of n!/10^n.

Terms

a(0) =1a(1) =10a(2) =50a(3) =500a(4) =1250a(5) =2500a(6) =12500a(7) =125000a(8) =156250a(9) =1562500a(10) =1562500a(11) =15625000a(12) =39062500a(13) =390625000a(14) =1953125000a(15) =3906250000a(16) =2441406250a(17) =24414062500a(18) =122070312500a(20) =610351562500