Determine ϕ(10n)\phi(10^n)ϕ(10n).
4⋅10n−14 \cdot 10^{n-1}4⋅10n−1
10n−110^n - 110n−1
2⋅10n−12 \cdot 10^{n-1}2⋅10n−1
5n5^n5n