0 20971
1 50232
2 102345
3 223459
4 212312
5 101102
6 211223
7 110212
8 98101
9 80983
10 170138
11 841395
12 408752
13 889984 *maximum
14 879840
15 758392
16 522717
17 217055
18 49552
19 103584
20 235927
21 111172
22 110521
23 95211
24 52103
25 20971
Now I have discovered a significantly longer loop starting with 204099163.
Update (3 Nov 2012): There exists an intermediate length-85 loop starting with 17175432.
Update (3 Nov 2012): There exists an intermediate length-85 loop starting with 17175432.