function gap(gap, start, end){
 var arr = [];
 var counter = [];
 var result;
 for(var x = start; x <= end; x++){
  if(x % 2 == 1){
   arr.push(x)
  }
 }
 for(var cache = arr.length, j = cache ; j >= 0; j--){
  for(var i = 2; i <= Math.sqrt(arr[j]); i++){
   if(arr[j] % i === 0){
    if(i != arr[j]/i || i * i == arr[j]){
      counter.push(arr[j] / i)
      arr.splice(j, 1)
      break;
    }
   }
  }

  if((arr[j+1] - arr[j]) == gap){
   result = [arr[j], arr[j+1]]
  }else if (result == undefined){
   result = null
  }
 }

 return result
}