555

Not sure what you want with “555.” Do you mean:

• math/number theory about the number 555, or
• the 555 timer IC (electronics), or
• something else (like a page/problem ID)?

If you’re studying math, here are quick facts about 555 and a tiny practice quiz:

• Prime factorization: 555 = 3 × 5 × 37
• Positive divisors: 1, 3, 5, 15, 37, 111, 185, 555
• Number of divisors d(555) = 8
• Sum of all divisors σ(555) = 912 (sum of divisors), so sum of proper divisors = 912 − 555 = 357
• Euler’s totient φ(555) = 296
• Example gcd: gcd(555, 1000) = 5
• Example modulo: 555 ≡ 2 (mod 7)

Mini-quiz (you can answer, I’ll check):

1. What is the prime factorization of 555?
2. How many positive divisors does 555 have?
3. What is φ(555)?
4. What is the sum of the proper divisors of 555?
5. Is 555 a perfect number?

If you meant the 555 timer IC or something else, tell me and I’ll tailor accordingly.