Q: Compute τ(12), σ(12), μ(12), φ(12). 12 = 2²×3. τ: (2+1)(1+1) = 6 divisors (1,2,3,4,6,12). σ: (2³-1)/(2-1) × (3²-1)/(3-1) = 7×4 = 28. μ(12): 2² divides → μ = 0 (not squarefree!). φ(12) = 4. All from prime exponents!