555

Do you mean: A) The number 555 (math), or B) The 555 timer IC (electronics)?

If you’re prepping for exams, here are quick cheats for both:

A) 555 as a number (math)

• Prime factorization: 555 = 3 × 5 × 37
• Divisors: 1, 3, 5, 15, 37, 111, 185, 555
• Sum of divisors (including 555): 1+3+5+15+37+111+185+555 = 912
• Sum of proper divisors: 912 − 555 = 357 → 357 < 555, so 555 is a deficient number
• Binary: 555 = 1000101011₂
• In Roman numerals: DLV

If you want, I can give you a quick practice problem or derive more properties (e.g., modulo arithmetic, divisibility tests, etc.).

B) 555 timer IC (electronics)

• Pinout (simplified):
  • 1 GND
  • 2 Trigger
  • 3 Output
  • 4 Reset
  • 5 Control Voltage
  • 6 Threshold
  • 7 Discharge
  • 8 VCC
• Modes:
  • Monostable (one-shot): output goes high for a time T = 1.1 × R × C
  • Astable (oscillator):
    • T_high = 0.693 × (R_A + R_B) × C
    • T_low = 0.693 × R_B × C
    • Period T = 0.693 × (R_A + 2R_B) × C
    • Frequency f = 1 / T
• Quick tips: Use proper decoupling capacitor on VCC (0.1 μF nearby), keep trigger capacitor and wiring short to avoid false triggering.

Tell me which context you meant, and what exact topic or problem you’re working on, and I’ll tailor a quick study guide or solve a sample problem.