a(0) = 0; a(n) = a(n/5)/5 if n = a(n/5) = 0 (mod 5); a(n) = a(n-1)+1 otherwise.

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =4a(5) =5a(6) =6a(7) =7a(8) =8a(9) =9a(10) =10a(11) =11a(12) =12a(13) =13a(14) =14a(15) =15a(16) =16a(17) =17a(18) =18a(19) =19a(20) =20a(21) =21a(22) =22a(23) =23a(24) =24a(25) =1a(26) =2a(27) =3a(28) =4a(29) =5