Which of the following numbers will replace the question mark (?) in the given series?
7, 13, ?, 145, 721, 4321
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 37.
Given series: 7, 13, ?, 145, 721, 4321
7 × 2 - 1 = 13; 13 × 3 - 2 = 37; 37 × 4 - 3 = 145; 145 × 5 - 4 = 721; 721 × 6 - 5 = 4321