Exercise · ZW-MULTIPLICATIVE-ARITHMETIC-FUNCTION-001 · ★☆☆ Basic
What is the value of \(\tau(12)\)?
Choose one option.
Show answer
- B. 6
Explanation
The positive divisors of 12 are 1, 2, 3, 4, 6, and 12, so there are six. The option of 4 counts only the divisors up to 4.
Review the concept: Multiplicative arithmetic function
An arithmetic function \(f\) is multiplicative if \(f(1)=1\) and \(f(mn)=f(m)f(n)\) whenever \(\gcd(m,n)=1\). Its behavior is determined by its values on prime powers.
\[f(mn)=f(m)f(n)\text{ if }\gcd(m,n)=1\]
More practice problems: multiplicative arithmetic function
- ZW-MULTIPLICATIVE-ARITHMETIC-FUNCTION-002 If f is multiplicative and gcd(m,n)=1, which expression equals f(mn)?
- ZW-MULTIPLICATIVE-ARITHMETIC-FUNCTION-003 What is the value of τ(p^3) for a prime p?
- ZW-MULTIPLICATIVE-ARITHMETIC-FUNCTION-004 Which of these functions is not multiplicative?
- ZW-MULTIPLICATIVE-ARITHMETIC-FUNCTION-005 If f is multiplicative, what is f(1)?
- ZW-MULTIPLICATIVE-ARITHMETIC-FUNCTION-006 If τ(n)=12 and n=2^2· 3^?, what is the exponent of 3?
- ZW-MULTIPLICATIVE-ARITHMETIC-FUNCTION-007 Compute τ(2^4· 5^2).
- ZW-MULTIPLICATIVE-ARITHMETIC-FUNCTION-008 If f is multiplicative with f(2)=3 and f(5)=4, what is f(10)?
- ZW-MULTIPLICATIVE-ARITHMETIC-FUNCTION-009 When computing τ(4) as τ(2)·τ(2), why does the multiplicativity rule not apply?