What number comes next: 1, 5, 14, 30, 55, ___?
Correct answer: C. 91
The differences are 4, 9, 16 and 25, which are perfect squares (2², 3², 4², 5²). The next difference is 6² = 36, so 55 + 36 = 91. Each term is the sum of the squares from 1² up to that point.
hard