Find the missing number in the series: 1, 7, 25, 61, 121, ?, 337

A205

B211 ✓ Correct

C209

D208

Correct answer: (B) 211

Explanation

The missing number is 211.

The differences are 6, 18, 36, 60, 90, 126.

These differences themselves rise by 12, 18, 24, 30, 36.

After 121 the next difference is 90, so 121 + 90 = 211.

Check: 211 + 126 = 337.

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