Three of the given four numbers are similar in a certain manner while one is…

Answer: 261 is the odd one out.

Reason: Three of the numbers (233, 277, 271) are prime numbers, meaning they have no divisors other than 1 and themselves. The number 261 is not prime.

• Check 261 for divisibility by 3: the digit sum is 2 + 6 + 1 = 9, which is divisible by 3, so 261 is divisible by 3 and therefore composite.

• Factorisation: 261 = 3 × 87 and 87 = 3 × 29, so 261 = 9 × 29, confirming it is composite.

• The other numbers (233, 271, 277) are not divisible by small primes and are prime numbers, so 261 is the only composite number and thus the odd one out.