In the sequence a, bb, ccc, dddd, eeeee, ..., what is the letter at the 126th…

Answer: p

The sequence is formed by writing the kth alphabet letter k times:
a (1 time), b (2 times), c (3 times), and so on.

We need the letter at the 126th position in the expanded sequence.

Letters up to the 15th block = 1 + 2 + ... + 15 = 15 × 16 / 2 = 120.

So positions 121 through 136 belong to the 16th block. The 16th letter is p.

Therefore, the letter at the 126th position is p.