555

Not sure what you want about 555. Do you mean:

• math (number properties, conversions, practice problems), or
• electronics (555 timer IC), or something else?

Here are quick math starters you can use right away:

• Prime factorization: 555 = 3 × 5 × 37
• Divisors: 1, 3, 5, 15, 37, 111, 185, 555 (8 divisors)
• Sum of divisors (including n): 912
• Euler totient: φ(555) = 288
• Binary: 555 = 1000101011₂
• Hexadecimal: 555 = 0x22B
• Roman numerals: 555 = DLV
• Quick mod example: 555 mod 7 = 2

A couple of quick practice problems you can try:

• Find gcd(555, 111).
• Verify φ(555) = φ(3) × φ(5) × φ(37) = 2 × 4 × 36 and compare to 288.
• Convert 555 to binary again by the repeated-divisions method.

If you meant the 555 timer IC, I can give you a concise overview and formulas for astable and monostable modes and example calculations. Tell me which topic you’re focusing on and your level, and I’ll tailor a set of problems or a quick review.