Problem 1458
Group the consecutive counting numbers as follows: (1), (2, 3), (4, 5, 6), (7, 8, 9, 10), . . Notice that there is one number in the first group, two numbers in the second group, three in the third, etc. What is the sum of the numbers in the 100th and 101st groups?
In other words, the sum of the numbers in the second and third groups is 2 + 3 + 4 + 5 + 6 = 20
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