In R2020a, you need to edit line 173 of arithenco to change
if ~all(seq > 0) || ~all(isfinite(seq)) || ~isequal(seq, round(seq)) || ...
to be >= 0 instead of > 0
and you need to change line 67
symbol = seq(k);
to
symbol = seq(k) + 1;
I might have missed some changes.
I would suggest to you that it would be far more robust to simply add 1 to all elements of your sequence,
[2 2 2 1 0 1] + 1
