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A123509 Rohrbach's problem: a(n) is the largest integer such that there exists a set of n integers that is a basis of order 2 for (0, 1, ..., a(n)-1).

Table of values

n a(n)
1 1
2 3
3 5
4 9
5 13
6 17
7 21
8 27
9 33
10 41
11 47
12 55
13 65
14 73
15 81
16 93
17 105
18 117
19 129
20 141
21 153
22 165
23 181
24 197
25 213

List of values

[1, 3, 5, 9, 13, 17, 21, 27, 33, 41, 47, 55, 65, 73, 81, 93, 105, 117, 129, 141, 153, 165, 181, 197, 213]