What do you call a fish without an eye?

Find The Next Number in this series.
1, 2, 6, 42, 1806 ?

An exterior architect is asked by a builder to plant seven trees in a manner that there are exactly six rows of trees in a straight line and each row has three trees in particular.

How will he do it?

How can you make the following equation true by drawing only one straight line: 5+5+5=550 ?

Mr. Buttons was all set to go to the village of Buttonland to meet his friend. So, he packed his bags and left for the village at 5 in the morning. Upon travelling on a road for miles, he came across a point where the road diverged into two. He was confused on which road to take. He gazed around and he saw two owls sitting on a branch. He thought he could ask for directions for the village from the two owls. So he went to the tree. There he saw a sign which read, "One owl always lies, and one is always truthful. They both fly away if you ask them more than 1 question."
Mr. Buttons was caught in the dilemma of what to ask? And from which owl to ask, since he only had one question. What should Mr. Buttons ask?

What begins with T, ends with T, and has T in it?

A tree doubled in height each year until it reached its maximum height over the course of ten years. How many years did it take for the tree to reach half its maximum height?

What has many teeth, but cannot bite?

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

The more you take me, the more you leave me behind.
Who Am I?