Source code in the icon programming language

procedure main()
every i := 5 | 50 | 255 | 1285 | 9000 do
  write(i," = ",binary(i))
end

procedure binary(n)                      #: return bitstring for integer n
static CT, cm, cb
initial {
   CT := table()                         # cache table for results
   cm := 2 ^ (cb := 4)                   # (tunable) cache modulus & pad bits 
   }   

b := ""                                  # build reversed bit string
while n > 0 do {                         # use cached result ...
   if not (b ||:= \CT[1(i := n % cm, n /:= cm) ]) then {                     
      CT[j := i] := ""                   # ...or start new cache entry
      while j > 0 do 
         CT[i] ||:=  "01"[ 1(1+j % 2, j /:= 2 )]
      b ||:= CT[i] := left(CT[i],cb,"0") # finish cache with padding
      }
   }
return reverse(trim(b,"0"))              # nothing extraneous
end