555

Not sure what you want about 555. Here are quick, exam-ready facts you can use in math, base conversions, or electronics. Tell me which direction you want or I can make a practice question set.

Math and number properties

• Factorization: 555 = 3 × 5 × 37 (all distinct, so it's squarefree)
• Divisibility: divisible by 3 and 5; 555 ÷ 15 = 37
• Harshad (Niven) number in base 10: 5+5+5 = 15, and 555 ÷ 15 = 37
• Palindrome: yes (reads the same forward/backward)
• Base representations:
  • Binary: 555 = 1000101011₂
  • Octal: 555 = 1053₈
  • Hexadecimal: 555 = 0x22B
• Roman numeral: DLV (500 + 50 + 5)

Electronics (if you meant the 555 timer IC)

• Common configurations: astable (oscillator) and monostable (one-shot)
• Astable frequency: f ≈ 1.44 / [(RA + 2RB) C]
• Monostable pulse width: t ≈ 1.1 × R × C
• Pins: 1 = GND, 2 = Trigger, 3 = Output, 4 = Reset, 5 = Control, 6 = Threshold, 7 = Discharge, 8 = Vcc (varies by package)

Quick practice questions (pick one area)

• Math: Factorize 555 and verify it's squarefree.
• Base conversions: Convert 555 to decimal → binary → hex.
• Electronics: If you use a 555 timer in astable mode with RA = 1 kΩ, RB = 2 kΩ, and C = 1 µF, what is the approximate frequency?

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