555

What would you like to do with 555? math practice, electronics (555 timer), or something else?

If you want quick math notes and a couple of problems, here you go:

• Factorization: 555 = 3 × 5 × 37
• Divisors: 1, 3, 5, 15, 37, 111, 185, 555 (eight divisors)
• Digit sum: 5 + 5 + 5 = 15; digital root = 6
• Roman numeral: DLV
• Binary: 1000101011

Practice problems:

1. Sum of the first 10 multiples of 555: S = 555 × (10×11)/2 = 555 × 55 = 30,525
2. gcd(555, 1000): 5
3. How many divisors does 555 have? 8

If you’re studying the 555 timer IC for electronics, I can give a quick overview and example circuits. Just tell me which you prefer.