digits([arg]) := block(
[n: first(arg), b: if length(arg) > 1 then second(arg) else 10, v: [ ], q],
do (
[n, q]: divide(n, b),
v: cons(q, v),
if n=0 then return(v)))$
binary(n) := simplode(digits(n, 2))$
binary(9000);
/*
10001100101000
*/