What should come place of the question mark(?) in the following number series?17, 18 , 26, 53 , 117, ? , 458

To find the missing number in the series, let's analyze the pattern:

The difference between the first two numbers is 18 - 17 = 1. The difference between the second and third numbers is 26 - 18 = 8. The difference between the third and fourth numbers is 53 - 26 = 27. The difference between the fourth and fifth numbers is 117 - 53 = 64.

From this pattern, we can see that the differences are increasing by a factor of 8 each time. So, the difference between the fifth and sixth numbers should be 64 + 8 = 72.

To find the missing number, we add 72 to the fifth number: 117 + 72 = 189.

Therefore, the missing number in the series is 189.