Find the next number in the sequence

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

What has lots of eyes, but can’t see?

Name a key which is hardest to turn.

The square root of number 121 is "11". What is the square root of the number "12345678987654321."?

You need to remove two matchsticks to make the below equation true. Can you do it ?

You walk into a room and see a bed. On the bed, there are two dogs, five cats, a giraffe, six cows, and a goose. There are also three doves flying above the bed. How many legs are on the floor?

He digs out tiny caves and stores gold and silver in them. He also built bridges of silver and made crowns of gold. They are the smallest you could imagine. Sooner or later everybody needs his help, yet many people are afraid to let him help them. Who is he?

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

The product of three consecutive numbers is 7980.
Then the sum of these consecutive numbers would be?

Replace the question mark with the correct number.