555

Could mean a few different things. Do you want some math stuff about the number 555, or something else (like Thai texting slang where 555 means laughing), or a problem where 555 is used?

If you’re after math properties (number theory), here are quick facts and a couple of exam-style problems:

Key facts about 555

• Prime factorization: 555 = 3 × 5 × 37 (it's squarefree)
• Divisors: 1, 3, 5, 15, 37, 111, 185, 555 (8 divisors)
• Sum of divisors σ(555) = 912
  • Compute: (1+3)(1+5)(1+37) = 4 × 6 × 38 = 912
• Euler’s totient: φ(555) = 555 × (1 − 1/3) × (1 − 1/5) × (1 − 1/37) = 288
• Binary representation: 555 = 1000101011₂
• Decimal digit sum: 5+5+5 = 15

Example exam-style questions

1. Find φ(555).

   • Answer: 288

2. List all divisors of 555.

   • Answer: 1, 3, 5, 15, 37, 111, 185, 555

3. Compute the sum of divisors σ(555).

   • Answer: 912

4. Is 555 squarefree?

   • Answer: Yes (its prime factors are distinct)

5. What is 555 modulo 7?

   • 7 × 79 = 553, so 555 ≡ 2 (mod 7)

If you want, tell me your course (e.g., number theory, algebra, discrete math) and the type of problem you’re studying, and I’ll tailor practice questions and step-by-step solutions. Also happy to explain the “555 means laughing” angle if that’s what you need.