555

Not sure what you want with “555.” Here are a few quick possibilities. Tell me which you mean, or what you’d like to focus on.

If you mean the number 555 (math practice):

• Factorization: 555 = 3 × 5 × 37
• Number of divisors: (1+1)(1+1)(1+1) = 8 Divisors: 1, 3, 5, 15, 37, 111, 185, 555
• Sum of divisors (σ): (1+3)(1+5)(1+37) = 4 × 6 × 38 = 912
• Euler’s totient φ(555): φ(555) = 555 × (1−1/3) × (1−1/5) × (1−1/37) = 288
• Quick practice problems:
  1. Find the modular inverse of 555 modulo 7. Hint: 555 ≡ 2 (mod 7); solve 2x ≡ 1 (mod 7) → x ≡ 4 (mod 7).
  2. Verify the divisors and the sum of divisors you obtain above.

If you mean “555” as Thai slang (555 = haha):

• 5 is pronounced “ha” in Thai, so 555 = “hahaha.” This is just internet slang, not exam content.

If you meant something else (a problem number, a concept, etc.), tell me the subject and topic and I’ll tailor a quick set of questions and solutions.