In what year was Sikkim formally incorporated as a state

Select the number from among the given option that can replace the question mark (?) in the following series.

4, 21, 86, 261, 526, ?

Find the missing number.

Find the missing number. 

Select the missing number from the given alternatives:

Study the given matric carefully and select the number from among the given options that can replace the question mark (?) in it.

What will come in the place of question mark?

Find the missing term:

What number should replace the question mark? 

Select the missing number from the given responses.

Choose the correct alternative that will complete the given number series. 2, 9, 28, 65, ?, 217