Consider the following series:

`0,1,2,3,4,5,6,7,8,9,10,22,11,20,13,24...`There is nothing special between numbers `0` and `10`. 

Let's start with the number `10` and derive the sequence. `10` has digits `1` and `0`. The next possible number that does not have a `1` or a `0` is `22`. All other numbers between `10` and `22` have a `1` or a `0`. 

From `22`, the next number that does not have a `2` is `11`. Note that `30` is also a possibility because it is the next *higher* number that does not have a `2`, but we must select  the *lowest* number that fits and **is not already in the sequence**. 

From `11`, the next lowest number that does not have a `1` is `20`. 

From `20`, the next lowest number that does not have a `2` or a `0` is `13`, then `24` , then `15` and so on. 

Once a number appers in the series, it cannot appear again. 

You will be given an index number and your task will be return the element at that position. See test cases for more examples.

Note that the test range is `n <= 500`. 

Good luck!

If you like this Kata, please try:

[Sequence convergence](https://www.codewars.com/kata/59971e64bfccc70748000068)

[https://www.codewars.com/kata/unique-digit-sequence-ii-optimization-problem](https://www.codewars.com/kata/unique-digit-sequence-ii-optimization-problem)

```python

USER_FILENAME = "<user_code>"
import sys, json, builtins
import math, heapq, bisect, itertools, functools, collections, statistics, fractions, decimal, operator, array, random, re, string, os, pathlib
try:
    import resource as _res
except Exception:
    _res = None
from collections import Counter, defaultdict, deque, OrderedDict
from functools import lru_cache, reduce
from itertools import accumulate, permutations, combinations, product
from math import gcd, ceil, floor, sqrt
from decimal import Decimal
try:
    from typing import *
except Exception:
    pass
try:
    sys.setrecursionlimit(1_000_000)
except Exception:
    pass
try:
    import site as _site
    try:
        _sys_sites = _site.getsitepackages() if hasattr(_site, "getsitepackages") else []
        for _p in _sys_sites:
            if _p and _p not in sys.path:
                sys.path.append(_p)
    except Exception:
        pass
    try:
        _usp = _site.getusersitepackages()
        if isinstance(_usp, str):
            _usp = [_usp]
        for _p in _usp:
            if _p and _p not in sys.path:
                sys.path.append(_p)
    except Exception:
        pass
except Exception:
    pass

def _disabled_input(*args, **kwargs):
    raise RuntimeError("input() is disabled in callable mode")
builtins.input = _disabled_input

ns = {"__name__": "__judge__"}  # prevent if __name__ == "__main__" blocks
for _k, _v in list(globals().items()):
    if not _k.startswith("_"):
        ns[_k] = _v
_CODE = 'masks = [0] * 10\nfor i in range(10 ** 4):\n    for c in str(i):\n        masks[int(c)] |= 1 << i\n\ndef find_num(n):\n    seq, x = 1, 0\n    for j in range(n):\n        M = seq\n        for m in masks:\n            if x & m:\n                M |= m\n        x = ~M & (M+1)\n        seq |= x\n    return x.bit_length() - 1'
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

_target = None
_fn_name = 'find_num'
if _fn_name:
    if "Solution" in ns:
        try:
            _obj = ns["Solution"]()
            if hasattr(_obj, _fn_name):
                _target = getattr(_obj, _fn_name)
        except Exception:
            _target = None
    if _target is None and _fn_name in ns and callable(ns[_fn_name]):
        _target = ns[_fn_name]
# Fallback: if there's exactly one user-defined function, use it
if _target is None:
    _cands = [v for k, v in ns.items() if callable(v) and getattr(v, "__module__", "") in ("__judge__", "__main__")]
    _user_funcs = [c for c in _cands if getattr(c, "__name__", "").startswith("_") is False]
    if len(_user_funcs) == 1:
        _target = _user_funcs[0]
if _target is None:
    raise RuntimeError(f"Could not resolve callable '{_fn_name}'")

_raw = sys.stdin.read().strip()
if _raw:
    _parsed = json.loads(_raw)
    if isinstance(_parsed, dict):
        _kwargs = _parsed.get("kwargs", {})
        _args = _parsed.get("args", [])
    else:
        _args, _kwargs = _parsed, {}
else:
    _args, _kwargs = [], {}
if not isinstance(_args, (list, tuple)):
    _args = [_args]
_res = _target(*_args, **_kwargs)
try:
    sys.stdout.write(repr(_res) + "\n")
except Exception:
    pass

```

Measured memory_bytes: 5426