retrive int[] of all grays code combinations

getGrays.cs

private IEnumerable<int[]> getGrays(int n) {
    //if n is > 24 memory fails
    if (n <= 0 || n > 24) { return null; }
    var ar = new List<string> { "0", "1" };
    for (var i = 2; i < 1 << n; i = i << 1) {
        for (var j = i - 1; j >= 0; j--) { ar.Add(ar[j]); }
        for (var j = 0; j < i; j++) { ar[j] = $"0{ar[j]}"; }
        for (var j = i; j < 2 * i; j++) { ar[j] = $"1{ar[j]}"; }
    }
    var returnAr = new List<int[]>();
    foreach (var s in ar) {
        var chars = s.ToCharArray();
        var tempIntArray = new int[chars.Length];
        for (var i = 0; i < chars.Length; i++) {
            var tempInt = int.Parse(chars[i].ToString());
            tempIntArray[i] = tempInt;
        }
        returnAr.Add(tempIntArray);
    }
    return returnAr;
}