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问题: 2,5,10,17,26,37,50,65……2501是第几个数

要写出规律

解答:

2,5,10,17,26,37,50,65……,2501是第几个数?

2 = 1^2 + 1
5 = 2^2 + 1
10 = 3^2 + 1
......
an = n^2 + 1

所以有
2501 = n^2 + 1
n = 50