[рони]

argab,
примерно так

<script>
   function fn(num)
   {  var obj = {};
      var a = num/2|0, b = num - a;
      obj[a] = a > 1 ? fn(a) : a;
      obj[b+' '] = b > 1 ? fn(b) : b;
      return obj
   }
   console.log(fn(9))
   document.write(JSON.stringify(fn(9),null,1))
</script>