555

Do you want a quick math-only note on 555, or something else (electronics with the 555 timer, Roman numerals, base conversions, etc.)?

Here are a few quick math facts about 555:

• Prime factorization: 555 = 3 × 5 × 37 (three distinct primes).
• Divisors: 1, 3, 5, 15, 37, 111, 185, 555.
• Sum of digits: 5+5+5 = 15, so 555 is divisible by 15. It’s a Harshad (Niven) number because 555 / 15 = 37.
• It’s a sphenic number (product of three distinct primes): 3 × 5 × 37.
• Binary representation: 555 = 1000101011₂.
• Roman numerals: 555 = DLV.
• Sum of divisors function: σ(555) = (1+3) × (1+5) × (1+37) = 4 × 6 × 38 = 912. So sum of proper divisors is 912 − 555 = 357 (555 is deficient).
• Is 555 a square, prime, or automorphic? No to all—it's not prime, not a square, and 555² ends with 025, not 555, so not automorphic.

If you want, I can turn this into quick practice questions (e.g., “list all divisors, verify Harshad, compute σ(n), convert to binary, etc.”) or dive into another interpretation (555 timer circuit basics, Roman numeral usage, or base-2/other-base conversions). Which would you prefer?