What will come in place of question mark in the following number series ?

1, 3, 7, 15, ?, 63, 127

A 22

B 25

C 29

D 31

Answer & Explanation
Option: [D]

The pattern is

2¹ - 1 = 1

2² - 1 = 3

2³ - 1 = 7

2⁴ - 1 = 15

2⁵ - 1 = 31

2⁶ - 1 = 63

2⁷ - 1 = 127

So, 31 will replace the question mark.

Take Mock Tests

Political Science Mock Test – 42	Start Test
History Test – 190	Start Test
Quantitative Aptitude Test	Start Test!
Trigonometry - Mock Test	Start Test!
Data Interpretation - Mock Test	Start Test!
General Awareness - Mock Test	Start Test!
Reasoning Ability - Mock Test	Start Test!
Englist(Antonyms) Mock Test 1	Start Test!
Quantitative Aptitude (Percentage) Mock Test	Start Test!
Economy Mock Test 1	Unlock Test!
Economy Mock Test 2	Unlock Test!
Economy Mock Test 3	Unlock Test!
Economy Mock Test 4	Unlock Test!
Economy Mock Test 5	Unlock Test!
Books & Authors - Test 2	Unlock Test!