import sys
readline=sys.stdin.readline
class Prime:
def __init__(self,N):
assert N<=10**8
self.smallest_prime_factor=[None]*(N+1)
for i in range(2,N+1,2):
self.smallest_prime_factor[i]=2
n=int(N**.5)+1
for p in range(3,n,2):
if self.smallest_prime_factor[p]==None:
self.smallest_prime_factor[p]=p
for i in range(p**2,N+1,2*p):
if self.smallest_prime_factor[i]==None:
self.smallest_prime_factor[i]=p
for p in range(n,N+1):
if self.smallest_prime_factor[p]==None:
self.smallest_prime_factor[p]=p
self.primes=[p for p in range(N+1) if p==self.smallest_prime_factor[p]]
def Factorize(self,N):
assert N>=1
factors=defaultdict(int)
if N<=len(self.smallest_prime_factor)-1:
while N!=1:
factors[self.smallest_prime_factor[N]]+=1
N//=self.smallest_prime_factor[N]
else:
for p in self.primes:
while N%p==0:
N//=p
factors[p]+=1
if N<p*p:
if N!=1:
factors[N]+=1
break
if N<=len(self.smallest_prime_factor)-1:
while N!=1:
factors[self.smallest_prime_factor[N]]+=1
N//=self.smallest_prime_factor[N]
break
else:
if N!=1:
factors[N]+=1
return factors
def Divisors(self,N):
assert N>0
divisors=[1]
for p,e in self.Factorize(N).items():
pow_p=[1]
for _ in range(e):
pow_p.append(pow_p[-1]*p)
divisors=[i*j for i in divisors for j in pow_p]
return divisors
def Is_Prime(self,N):
return N==self.smallest_prime_factor[N]
def Totient(self,N):
for p in self.Factorize(N).keys():
N*=p-1
N//=p
return N
def Mebius(self,N):
fact=self.Factorize(N)
for e in fact.values():
if e>=2:
return 0
else:
if len(fact)%2==0:
return 1
else:
return -1
N=int(readline())
A=list(map(int,readline().split()))
Pr=Prime(2*10**6)
cnt=A.count(1)
for a in A:
if a==1:
continue
if Pr.Is_Prime(a+1) and cnt:
ans=cnt+1
ans_lst=[1]*cnt+[a]
break
else:
if cnt>=2:
ans=cnt
ans_lst=[1]*cnt
else:
for i in range(N):
for j in range(i+1,N):
if Pr.Is_Prime(A[i]+A[j]):
ans=2
ans_lst=[A[i],A[j]]
break
else:
continue
break
else:
ans=1
ans_lst=[A[0]]
print(ans)
print(*ans_lst)#include <bits/stdc++.h>
using namespace std;
using ll=long long;
using PII=pair<int,int>;
const int N=1e6+10;
int n;
int a[1010],t[N];
int cnt,num2,idx;
bool check(int x){
if(x==2) return 1;
for(int i=2,j=sqrt(x);i<=j;i++)
if(x%i==0) return 0;
return 1;
}
void tong(){
for(int i=1;i<=N;i++){
if(t[i]) a[++idx]=i;
}
}
void solve(){
cin >> n;
for(int i=1;i<=n;i++){
cin >> a[i];
if(a[i]==1) cnt++;
if(check(a[i]+1) && a[i]!=1) num2=a[i];
t[a[i]]++;
}
if(cnt==1 && num2){cout << 2 << endl << 1 << " " << num2; return ;}
if(cnt>=2){
if(num2){
cout << cnt+1 << endl;
while(cnt--) cout << 1 << " ";
cout << num2;
}else{
cout << cnt << endl;
while(cnt--) cout << 1 << " ";
}
return ;
}
tong();
for(int i=1;i<=idx;i++){
for(int j=1;j<=idx;j++){
if(i==j) continue;
if(check(a[i]+a[j])){cout << 2 << endl << a[i] << " " << a[j]; return ;}
}
}
cout << 1 << endl << a[1] << endl;
}
int main(){
ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
int t=1;
//cin >> t;
while(t--) solve();
return 0;
}
//make it count
//开ll了没Teddy and Tweety | Partitioning binary strings |
Special sets | Smallest chosen word |
Going to office | Color the boxes |
Missing numbers | Maximum sum |
13 Reasons Why | Friend's Relationship |
Health of a person | Divisibility |
A. Movement | Numbers in a matrix |
Sequences | Split houses |
Divisible | Three primes |
Coprimes | Cost of balloons |
One String No Trouble | Help Jarvis! |
Lift queries | Goki and his breakup |
Ali and Helping innocent people | Book of Potion making |
Duration | Birthday Party |
e-maze-in | Bricks Game |