Find the next number in the sequence

1, 2, 6, 21, 88, __?

Can you decipher these quotes by Albert Einstein?
Blf xzm mvevi hloev z kilyovn lm gsv ovevo lm dsrxs rg dzh xivzgvw.

You are in a room that has three switches and a closed door. The switches control three light bulbs on the other side of the door. Once you open the door, you may never touch the switches again. How can you definitively tell which switch is connected to each of the light bulbs?

Can you find a rabbit in the given picture?

There is an English word that can be used up to four times in a row without modifying the spelling and form a valid grammatical sentence.

Do you know what word is that?

John left on a horse on Thursday , was gone for two days, and came back on Thursday after completing his work. How did that happen?

Can you quickly find which two matchstick figures are identical?

Move four matchsticks to the below square to form three squares?

Railroad Crossing, look out for the cars. Can you spell that, without any R's ?

What is the riddle which can be asked all day with a different correct answer each time.