20 раз:
7, 17, 27, 37, 47, 57, 67, 87, 97
70, 71, 72, 73, 74, 75, 76, 77, 78, 79
1) 15 (A-B-F-Z)
2) 17 (A-B-D-E-F-Z или A-B-D-E-G-Z)
3) 15 (A-B-F-Z)