Puzzling Asked on June 22, 2021
Alice and Bob play a game, taking turns. Alice starts and writes an integer between 1 to 10 on a blackboard.
Then Bob adds any integer between 1 to 10 to this number and writes it on the blackboard.
When a three digit number is reached the game ends.
During the game the number of positive divisors of each integer written down by Alice are added up, the same applies for Bob.
If Alice has more divisors at the end she wins, otherwise Bob wins.
The divisors of the three digit number are not counted.
Is there a winning strategy for any of the players?
Example:
Alice 4 20 30 40 53 58 70 82 92 99 (number of divisors: 3+6+8+8+2+4+8+4+6+6=55)
Bob 12 22 31 48 57 68 75 88 96 100 (number of divisors: 6+4+2+10+4+6+6+8+12=58)
and Bob is the winner in this case.
After recalculating the table I believe that there is a winning strategy for A, as follows:
A chooses 1 first and ends up winning by 1 point.
See Tables below showing the way an optimal game could progress. Spoiler space added as I cant work out how to hide a table.
An optimal game would progress as follows (Asc and Bsc are the scores for A and B after each move):
Mov Pl. Num Sum Asc BSc
1 A 1 1 1 0
2 B 9 10 1 4
3 A 2 12 7 4
4 B 1 13 7 6
5 A 7 20 13 6
6 B 4 24 13 14
7 A 6 30 21 14
8 B 6 36 21 23
9 A 6 42 29 23
10 B 7 49 29 26
11 A 7 56 37 26
12 B 4 60 37 38
13 A 1 61 39 38
14 B 9 70 39 46
15 A 2 72 51 46
16 B 8 80 51 56
17 A 10 90 63 56
18 B 9 99 63 62
The above was calculated using the following table showing the relative advantage in moving to any specific position (calculated using the algorithm described above).
Sum Div Adv
1 1 1
2 2 -2
3 2 -2
4 3 -1
5 2 -2
6 4 0
7 2 -2
8 4 0
9 3 -1
10 4 0
11 2 -2
12 6 4
13 2 2
14 4 -2
15 4 -2
16 5 -1
17 2 -4
18 6 0
19 2 -4
20 6 0
21 4 -2
22 4 -2
23 2 -4
24 8 6
25 3 1
26 4 -2
27 4 -2
28 6 0
29 2 -4
30 8 2
31 2 -4
32 6 0
33 4 -2
34 4 -2
35 4 -2
36 9 6
37 2 -1
38 4 -1
39 4 -1
40 8 3
41 2 -3
42 8 3
43 2 -3
44 6 1
45 6 1
46 4 -1
47 2 -3
48 10 5
49 3 5
50 6 -4
51 4 -6
52 6 -4
53 2 -8
54 8 -2
55 4 -6
56 8 -2
57 4 -6
58 4 -6
59 2 -8
60 12 10
61 2 2
62 4 -4
63 6 -2
64 7 -1
65 4 -4
66 8 0
67 2 -6
68 6 -2
69 4 -4
70 8 0
71 2 -6
72 12 8
73 2 -2
74 4 -2
75 6 0
76 6 0
77 4 -2
78 8 2
79 2 -4
80 10 4
81 5 -1
82 4 -2
83 2 -4
84 12 6
85 4 -2
86 4 -2
87 4 -2
88 8 2
89 2 -4
90 12 6
91 4 -2
92 6 0
93 4 -2
94 4 -2
95 4 -2
96 12 6
97 2 -4
98 6 0
99 6 6
Answered by Penguino on June 22, 2021
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