555

Could you tell me what you want to do with 555? Here are a few common angles:

• Math (number theory): 555 = 3 × 5 × 37. It’s divisible by 3 and 5 (sum of digits is 15; ends with 5). In binary, 555 is 1000101011. Roman numeral: DLV.
• Electronics (555 timer): In astable mode, f ≈ 1.44 / [(R_A + 2R_B) C], with t_high ≈ 0.693 (R_A + R_B) C and t_low ≈ 0.693 R_B C. In monostable mode, pulse width t ≈ 1.1 R C.
• Quick practice problem: Factor 555 (already: 3 × 5 × 37). If you want, I can give more problems.

Tell me your subject or what you’d like to practice, and I’ll tailor it.