Choose the number which is different from the others in the group.

Examining the numbers in the group: 131, 161, 151, 171

Each number has the pattern: first digit is 1, last digit is 1, with a middle digit varying.

The middle digits are:

• 131: middle digit is 3 (odd)
• 161: middle digit is 6 (even)
• 151: middle digit is 5 (odd)
• 171: middle digit is 7 (odd)

161 is the only number where the middle digit is even.

All other numbers (131, 151, 171) have odd digits in the middle position.

Therefore, 161 is different from the others in the group.