From the set {1, 2, 3 , 20} and make the three numbers into an increasing arithmetic sequence, then the sequence has the same number______ Group

From the set {1, 2, 3 , 20} and make the three numbers into an increasing arithmetic sequence, then the sequence has the same number______ Group

Because the sequence is incremental, when the tolerance is 1, the sequence can be 123234 When the tolerance is 2, the sequence is 135246357 When the tolerance is 3, the sequence is 147258369, 4710 14, 17, 20 are 14 cases, and so on, when the difference is 9, there are two cases of sequence 1, 10, 19; 2, 11, 20, the total case is 2 + 4 + 6 + 18 = 90. So the answer is 90