555

Do you want information about 555 in math, electronics (the 555 timer), or something else (like the 555 nm wavelength in color science)? Here are quick notes for a few common contexts:

Math

• 555 = 3 × 5 × 37 (square-free).
• Divisors: 1, 3, 5, 15, 37, 111, 185, 555.
• Sum of digits = 15, so divisible by 3 and by 5; 555/15 = 37.
• In hex: 0x22B; in binary: 1000101011.
• Decimal palindrome: 555 reads the same forwards and backwards.
• It’s a Harshad (Niven) number.

Electronics (555 timer IC)

• The NE555/LM555 is a versatile timer IC used in astable and monostable configurations.
• Key formulas (typical values):
  • Astable frequency: f ≈ 1.44 / [(R1 + 2R2) C]
  • High time: t_high ≈ 0.693 (R1 + R2) C
  • Low time: t_low ≈ 0.693 R2 C
  • Monostable pulse width: t ≈ 1.1 R C
• Pinout (common): 1 GND, 2 TRIG, 3 OUT, 4 RESET, 5 CTRL, 6 THR, 7 DISCH, 8 VCC.

Color science

• 555 nm is near the peak of human visual sensitivity (photopic luminous efficiency curve). It’s a greenish-yellow region.

If you tell me which context you’re studying, I can dive deeper, work through a problem, or give you a quick practice question.