🎴 Flashcard Mode

In the sequence 1, 2, 5, 6, the number 5 is the odd one out as it's the only prime number. Prime numbers are divisible only by 1 and themselves, whereas 1, 2, and 6 are not primes (1 is neither prime nor composite, 2 is actually prime, and 6 is composite). The pattern logic appears to be about number properties.