The string abbcccddddeeeee.... continuously repeats - with a repeating once, b repeating twice and so on, such that after the final z, the letters abbcccddddeeeee.... begin again.

What will be the 2010^{th} letter in the above pattern?

As a bonus, what will be the 2010th letter in the above pattern, if instead - after the final z, the next a repeats 27 times, then b repeats 28 times and so forth?

Once thru the alphabet uses 351 letters (1 + 26) * (26/2).

Five times thru will give the 1755th letter as a final "Z"

The 23 letters A..V use 253 letters.

Hence the 2010th letter will be "W".