Arrange the positive integers as follows: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. What's the 25th number on line 100? one 2、3 4、5、6 7、8、9、10 11、12、13、14、15
four thousand nine hundred and seventy-five
The first n rows have 1 + 2 + 3 +. + n = n (n + 1) / 2 numbers. The first 99 rows have 99 * 100 / 2 = 4950 numbers, so the 25th number in the 100th row is 4975 (= 4950 + 25)
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