555

Do you mean:

• the number 555 (math/number theory), or
• the 555 timer IC (electronics)?

If you meant the math 555:

• Prime factorization: 555 = 3 × 5 × 37
• Divisors: 1, 3, 5, 15, 37, 111, 185, 555 (8 divisors)
• Sum of divisors: σ(555) = (1+3)(1+5)(1+37) = 4×6×38 = 912
• Roman numeral: 555 = DLV
• Binary: 555 = 1000101011₂
• Hexadecimal: 0x22B
• Quick practice problem: Find the number of divisors and the sum of divisors of 555. Answer: 8 divisors; sum = 912.

If you meant the 555 timer IC:

• Modes: astable (generates a continuous square wave) and monostable (one-shot pulse)
• Pinout (common DIP-8): 1 = Ground (GND), 2 = Trigger, 3 = Output, 4 = Reset, 5 = Control Voltage, 6 = Threshold, 7 = Discharge, 8 = VCC
• Astable frequency: f ≈ 1.44 / ((R1 + 2R2) C)
• Astable duty cycle: D ≈ (R1 + R2) / (R1 + 2R2)
• Monostable pulse width: t ≈ 1.1 R C (depending on wiring)

Tell me which area you want, and I’ll tailor problems or a quick review for your exam.