555

Do you mean one of these?

• The number 555 (math properties)
• The 555 timer IC (electronics)
• Something else (Roman numerals, base conversions, area code, etc.)

If you want a quick math refresher:

• 555 = 3 × 5 × 37
• Sum of digits = 15 ⇒ divisible by 3 (and by 5), so 555 is composite
• In Roman numerals: DLV
• In binary: 1000101011
• In base 3: 202120_3

Tell me which topic you want, and I’ll tailor a short cheat-sheet or practice problems for your exam.