555

Do you mean the number 555 (math properties) or something else (like 555 meaning in Thai texting, which is laughter)? If you want math help, here are quick facts and a couple of practice ideas:

Quick facts about 555

• Prime factorization: 555 = 3 × 5 × 37
• Divisors: 1, 3, 5, 15, 37, 111, 185, 555
• Euler’s totient: φ(555) = φ(3)·φ(5)·φ(37) = 2·4·36 = 288
• Sum of divisors: σ(555) = (1+3)(1+5)(1+37) = 4×6×38 = 912
• Mod properties: 555 ≡ 0 (mod 5); 555 ≡ 6 (mod 9); not divisible by 11
• Representations: Roman numeral DLV; hex 0x22B; binary 1000101011

Two quick practice problems

1. How many integers k with 1 ≤ k ≤ 555 are coprime to 555? Answer: 288 (φ(555)).
2. Solve a CRT-style problem: find x such that x ≡ 2 (mod 3), x ≡ 1 (mod 5), x ≡ 4 (mod 37). The solution is x ≡ 257 (mod 555).

If you want, tell me what specific topic you’d like (factorization practice, divisors, modular arithmetic, CRT, etc.) and I’ll tailor problems and solutions.