> You have an extra card in your hand (a '1' as well as an ace).

Here's my updated results using a two-deck deck and 5000 simulated
hands per upcard.

Upcard  Bust    17      18      19      20      21      Natural
2      35.14%  13.66%  13.80%  13.18%  12.10%  12.12%   0.00%
3      37.96%  13.02%  12.72%  12.98%  12.10%  11.22%   0.00%
4      39.98%  13.40%  12.70%  11.70%  11.58%  10.64%   0.00%
5      40.70%  12.86%  12.66%  11.12%  11.94%  10.72%   0.00%
6      43.02%  16.74%  10.30%  10.20%   9.78%   9.96%   0.00%
7      26.36%  37.44%  13.18%   8.02%   7.84%   7.16%   0.00%
8      24.52%  12.68%  35.78%  13.42%   6.72%   6.88%   0.00%
9      23.64%  11.52%  11.98%  34.42%  11.88%   6.56%   0.00%
t      21.60%  11.60%  10.90%  11.22%  33.36%   3.98%   7.34%
j      21.30%  11.84%  10.94%  11.68%  32.84%   3.88%   7.52%
q      21.78%  11.26%  10.94%  11.20%  34.08%   3.68%   7.06%
k      20.60%  10.96%  10.34%  11.82%  34.60%   3.54%   8.14%
a      12.48%  13.40%  13.20%  12.82%  12.86%   4.84%  30.40%

Chris