Questions surface: https: //www.luogu.org/problem/P4091
题解:\[\begin{array}{l}
f(n) = \sum\limits_{i = 0}^n {\sum\limits_{j = 0}^i {{\rm{S}}(i,j) \cdot {2^{\rm{j}}} \cdot j!} } \\
= \sum\limits_{i = 0}^n {\sum\limits_{j = 0}^n {{\rm{S}}(i,j) \cdot {2^{\rm{j}}} \cdot j!} }
\end{array}\]
The formula \ [S (n, m) = \ frac {{\ sum \ limits_ {i = 0} ^ m {{{(- 1)} ^ i} {\ rm {\ cdot}} C_m ^ i} { \ rm {\ cdot}} {{(m - i)}! ^ n}}} {{m}} \] bring into
则\[{\rm{\backslash begin\{ array\} \{ l\} n\backslash begin\{ array\} \{ *\{ 20\} \{ l\} \} }}f(n) = \sum\limits_{i = 0}^n {\sum\limits_{j = 0}^n {{\rm{S}}(i,j) \cdot {2^{\rm{j}}} \cdot j!} = \sum\limits_{i = 0}^n {\sum\limits_{j = 0}^n {\sum\limits_{k = 0}^j {\frac{{{{( - 1)}^k}}}{{k!}} \cdot \frac{{{{(j - k)}^i}}}{{(j - k)!}}} \cdot {{\rm{2}}^{\rm{j}}}{\rm{\cdotj}}!} } } {\rm{n\{ }} = \sum {\rm{\_}}j = {\rm{\^}}n{\rm{ \{ }}{2^j}{\rm{\cdotj}}!\sum {\rm{\_}}k = 0{\rm{\^}}j{\rm{ \{ }}\sum {\rm{\_}}i = 0{\rm{\^}}n{\rm{ \{ }}\frac{{{{( - 1)}^k}}}{{k!}} \cdot \frac{{{{(j - k)}^i}}}{{(j - k)!}} = \sum {\rm{\_}}j = {\rm{\^}}n{\rm{ \{ }}{2^j}{\rm{\cdot}}j!\sum {\rm{\_}}k = 0{\rm{\^}}j{\rm{ \{ \backslash frac\{ \{ \{ }}( - 1){\rm{\^\{ \^}}k{\rm{\} \} \} \} }}k! \cdot {\rm{\} }}\frac{{\sum\limits_{i = 0}^n {{{(j - k)}^i}} }}{{(j - k)!}}{\rm{\} \} \} \} \} n\backslash end\{ array\} \backslash \backslash = }}\sum {\rm{\_}}j = {\rm{\^}}n{\rm{ \{ }}{2^j}{\rm{\cdot}}j!\sum {\rm{\_}}k = 0{\rm{\^}}j{\rm{ \{ \backslash frac\{ \{ \{ }}( - 1){\rm{\^\{ \^}}k{\rm{\} \} \} \} }}k! \cdot {\rm{\} }}\frac{{{{(j - k)}^{n + 1}} - 1}}{{(j - k)! \cdot (j - k - 1)}}{\rm{\} n\backslash end\{ array\} }}\]
令\[\begin{array}{l}
h(x) = \frac{{{{( - 1)}^x}}}{{x!}}\\
g(x) = \frac{{{x^{n + 1}} - 1}}{{x!{\rm{\cdot(x - 1)}}}}
\end{array}\]
Behind these two is the convolution of the line directly on ntt
#include<bits/stdc++.h> #define ms(x) memset(x,0,sizeof(x)) #define sws ios::sync_with_stdio(false) using namespace std; typedef long long ll; const int maxn=5e5+5; const double pi=acos(-1.0); const ll mod=998244353;///通常情况下的模数, const ll g=3;///模数的原根998244353,1004535809,469762049 ll qpow(ll a,ll n,ll p){ ll ans=1; while(n){ if(n&1) ans=ans*a%p; n>>=1; a=a*a%p; } return ans; } int rev[maxn]; void ntt(ll a[],int n,int len,int pd){ rev[0]=0; for(int i=1;i<n;i++){ rev[i]=(rev[i>>1]>>1 | ((i&1)<<(len-1))); IF (I < Rev [I]) the swap (A [I], A [Rev [I]]); } for ( int MID = . 1 ; MID <n-; MID = << . 1 ) { LL Wn of qpow = (G, (mod- . 1 ) / (MID * 2 ), MOD); /// primitive root root unit instead of IF (PD == - . 1 ) = Wn of qpow (Wn of, mod- 2 , MOD); / // inverse transform into the inverse element for ( int J = 0 ; J <n-; = J + 2 * MID) { LL W = . 1 ; for ( int K = 0;k<mid;k++){ ll x=a[j+k],y=w*a[j+k+mid]%mod; a[j+k]=(x+y)%mod; a[j+k+mid]=(x-y+mod)%mod; w=w*wn%mod; } } } if(pd==-1){ ll inv=qpow(n,mod-2,mod); for(int i=0;i<n;i++){ a[i]=a[i]*inv%mod; } } } ll a[maxn],b[maxn],c[maxn]; void solve(int n,int m){ int len=0,up=1; while(up<=n+m) up<<=1,len++; ntt(a,up,len,1); ntt(b,up,len,1); for(int i=0;i<up;i++) c[i]=1ll*a[i]*b[i]%mod; ntt(c,up,len,-1); } ll fa[maxn]; int main(){ int n,m; sws; cin>>n; fa[0]=1; a[0]=1; b[0]=1; for(int i=1;i<=n;i++){ fa[i]=1ll*fa[i-1]*i%mod; int t=(i&1)==1?-1:1; a[i]=(t*qpow(fa[i],mod-2,mod)+mod)%mod; if(i==1) b[1]=n+1; else { b [i] = (qpow (i, n + 1 , v) - 1 + v)% v * qpow (1LL * (i- 1 ) * f [i]% v, MOD 2 , v)% v; } } Solve (n, n); II ans = 0 ; for (II i = 0 ; i <= n; i ++ ) { ans = (ANS + qpow ( 2 , i, v) * f [i]% v * c [i]% v)% v; } Cout << ans << endl; }