The number of distinct prime factors of the largest 6-digit number is

The largest 6-digit number is 999999. Factorize: 999999 = 3³ × 7 × 11 × 13 × 37. Let's verify: 999999 = 999 × 1001 = (3 × 333) × (7 × 143) = (3 × 3 × 111) × (7 × 11 × 13) = 3³ × 37 × 7 × 11 × 13. The distinct prime factors are 3, 7, 11, 13, 37—that's 5 distinct primes. Hmm, only 5. Let me recheck: 999999 = 3 × 333333 = 3 × 3 × 111111 = 9 × 111111 = 9 × 3 × 37037 = 27 × 37037 = 27 × 7 × 5291 = 27 × 7 × 11 × 481 = 27 × 7 × 11 × 13 × 37. So 999999 = 3³ × 7 × 11 × 13 × 37. Distinct primes: {3, 7, 11, 13, 37} = 5 primes. So answer is 5, option (3).