555

Do you mean any of the following, or something else?

• Math: the number 555
• Electronics: the 555 timer IC
• A problem labeled 555 in your assignment

If you want quick math facts about 555:

• Factorization: 555 = 3 × 5 × 37
• Divisible by: 3 and 5 (and thus by 15)
• Not divisible by: 9, 25, etc.
• Hex: 0x22B
• Representations:
  • Sum of two consecutive integers: 277 + 278
  • Sum of three consecutive integers: 184 + 185 + 186
  • Sum of five consecutive integers: 109 + 110 + 111 + 112 + 113
• Example problem: gcd(555, 2025) = 15

If you want quick 555 timer basics:

• Pins (typical): 1 GND, 2 TRIG, 3 OUT, 4 RESET, 5 CTRL, 6 THRESH, 7 DISCH, 8 VCC
• Astable mode (oscillator): T ≈ 0.693 × (R1 + 2R2) × C; f ≈ 1.44 / ((R1 + 2R2) × C)
• Monostable mode (one-shot): Output high for T ≈ 1.1 × R × C
• Common use: pulse generation, tone generators, time delays

Tell me which context you’re after (or paste the exact question), and I’ll tailor the help.