My choice of number is 21


which leaves
00 01 02 03 04 05 06 07 08 09
10 11 12 13 14 15 16 17 1 8
20 22 23 26 27 28 29
30 31 32 33 34 35 36 37 38 39
40 41 42 43 44 45 46 47 48 49...