数论常见公式(不间断更新)

迪利克雷卷积

ϵ = μ ∗ 1 ⇔ ϵ ( n ) = ∑ d ∣ n μ ( d ) (1) \epsilon=\mu*1\Leftrightarrow \epsilon(n)=\sum_{d|n}\mu(d) \tag{1} ϵ=μ1ϵ(n)=dnμ(d)(1)
d = 1 ∗ 1 ⇔ d ( n ) = ∑ d ∣ n 1 (2) d=1*1\Leftrightarrow d(n)=\sum_{d|n}1 \tag{2} d=11d(n)=dn1(2)
σ = d ∗ 1 ⇔ σ ( n ) = ∑ d ∣ n d \sigma=d*1\Leftrightarrow \sigma(n)=\sum_{d|n}d σ=d1σ(n)=dnd
ϕ = μ ∗ I D ⇔ ϕ ( n ) = ∑ d ∣ n d ∗ μ ( n d ) \phi=\mu*ID \Leftrightarrow \phi(n)=\sum_{d|n}d * \mu(\frac{n}{d}) ϕ=μIDϕ(n)=dndμ(dn)

其他

g c d ( i j , j k , i k ) = g c d ( i , j ) g c d ( j , k ) g c d ( i , k ) g c d ( i , j , k ) (3) gcd(ij,jk,ik)=\frac{gcd(i,j)gcd(j,k)gcd(i,k)}{gcd(i,j,k)} \tag{3} gcd(ij,jk,ik)=gcd(i,j,k)gcd(i,j)gcd(j,k)gcd(i,k)(3)
d ( i j ) = ∑ x ∣ i ∑ x ∣ j [ g c d ( i , j ) = = 1 ] (4) d(ij)=\sum_{x|i}\sum_{x|j}[gcd(i,j)==1] \tag{4} d(ij)=xixj[gcd(i,j)==1](4)

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