555

Do you mean the number 555? Here are a few quick math-related facts you can use for exams, plus ideas for quick problems:

• Prime factorization: 555 = 3 × 5 × 37
• Divisors: 1, 3, 5, 15, 37, 111, 185, 555 (8 divisors)
• Sum of divisors (sigma function): σ(555) = 912
• Sum of proper divisors: 1 + 3 + 5 + 15 + 37 + 111 + 185 = 357
• Classification: since 357 < 555, 555 is a deficient number
• Harshad (Niven) check: sum of digits = 5+5+5 = 15; 555 ÷ 15 = 37, so 555 is a Harshad number in base 10
• Decimal digits: a repdigit (three 5s)
• Binary and hex representations: 555 in binary is 1000101011; in hex it is 0x22B
• Roman numeral: DLV

Sample quick problems you can practice:

• How many divisors does 555 have? (Answer: 8)
• Is 555 a perfect number, deficient, or abundant? (Answer: deficient)
• Show that 555 is divisible by the sum of its digits (Harshad test).
• Write 555 in binary and hex.
• Express 555 as a product of primes and verify the divisor list.

Would you like me to tailor these to a specific subject (e.g., number theory, algebra, or electronics with 555 timer circuits) or generate a short mock exam?