Find the next number in the sequence

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

Using the clues below, what four numbers am I thinking of?

The sum of all the numbers is 31.
One number is odd.
The highest number minus the lowest number is 7.
If you subtract the middle two numbers, it equals two.
There are no duplicate numbers.

What does the following represent?

N N N N N N N

A A A A A A A

C C C C C C C

In the attached figure, you can see a chessboard and two rooks placed on the chess board. What you have to find is the number of squares that do not contain the rooks. How many are there?

Find the Next Number in the Sequence

2 9 3 1 8 4 3 6 5 7 ?

If,
29 - 1 = 30
9 - 1 = 10
14 - 1 = 15

Based on similar logic, Can you prove that the below algebraic equation is true?
11 - 1 = 10 ?

Can you find out the total number of triangles in the given figure?

Three fair coins are tossed in the air and they land with heads up. Can you calculate the chances that when they are tossed again, two coins will again land with heads up?

Find the missing letter in the last circle logically in the given below picture.

Can you find the mistake in the below statement?