1 #include<iostream>
  2 #include<cstdio>
  3 #include<algorithm>
  4 #include<vector>
  5 #include<cstdlib>
  6 #include<cmath>
  7 #include<cstring>
  8 using namespace std;
  9 #define maxn 1010
 10 #define inf 0x7fffffff
 11 #define llg int
 12 #define yyj(a) freopen(a".in","r",stdin),freopen(a".out","w",stdout);
 13 llg n,m,ans,c[maxn],cnt1,cnt2,tot[maxn];
 14 llg d[maxn][maxn];
 15 inline int getint()
 16 {
 17     int w=0,q=0; char c=getchar();
 18     while((c<'0' || c>'9') && c!='-') c=getchar(); if(c=='-') q=1,c=getchar();
 19     while (c>='0' && c<='9') w=w*10+c-'0', c=getchar(); return q ? -w : w;
 20 }
 21
 22 struct DINIC
 23 {
 24     llg N;
 25     vector<llg>a[maxn],ba[maxn],val[maxn],stval[maxn];
 26     llg dl[maxn],deep[maxn];
 27     bool bj[maxn];
 28
 29     void link(llg x,llg y,llg z)
 30     {
 31         a[x].push_back(y),val[x].push_back(z); stval[x].push_back(z);
 32         a[y].push_back(x),val[y].push_back(0); stval[y].push_back(0);
 33         ba[x].push_back(a[y].size()-1),ba[y].push_back(a[x].size()-1);
 34     }
 35
 36     llg dfs(llg x,llg low)
 37     {
 38         llg va=0,inc=0;
 39         if (x==N) return low;
 40         llg w=a[x].size(),v;
 41         for (llg i=0;i<w;i++)
 42         {
 43             v=a[x][i];
 44             if (deep[x]+1==deep[v] && val[x][i]>0 && (va=dfs(v,min(low,val[x][i]))))
 45             {
 46                 val[x][i]-=va; val[v][ba[x][i]]+=va; inc+=va;
 47                 return va;
 48             }
 49         }
 50         if (!inc) deep[x]=-1;
 51         return 0;
 52     }
 53
 54     void fencen()
 55     {
 56         llg x,w,v; deep[0]=0;
 57         memset(bj,0,sizeof(bj));
 58         llg head=0,tail=1; dl[1]=0; bj[0]=1;
 59         do
 60         {
 61             x=dl[++head]; w=a[x].size();
 62             for (llg i=0;i<w;i++)
 63             {
 64                 v=a[x][i];
 65                 if (bj[v] || val[x][i]<=0) continue;
 66                 dl[++tail]=v;
 67                 deep[v]=deep[x]+1; bj[v]=1;
 68             }
 69         }while (head!=tail);
 70     }
 71
 72     llg dinic()
 73     {
 74         llg ans=0;
 75         while (1)
 76         {
 77             fencen();
 78             if (!bj[N]) break;
 79             ans+=dfs(0,inf);
 80         }
 81         return ans;
 82     }
 83
 84     void DFS(llg x)
 85     {
 86         bj[x]=1;
 87         tot[ans]++;
 88         d[ans][tot[ans]]=x;
 89         llg w=a[x].size(),v;
 90         for (llg i=0;i<w;i++)
 91         {
 92             v=a[x][i];
 93             if (v==0 || v==N || bj[v]) continue;
 94             if (stval[x][i]==val[x][i]) continue;
 95             DFS(v);
 96         }
 97     }
 98
 99     bool pd(llg x)
100     {
101         llg cs=0,w=a[x].size(),v;
102         for (llg i=0;i<w;i++)
103         {
104             v=a[x][i];
105             if (v==0 || v==N) continue;
106             if (bj[v] || val[x][i]==stval[x][i]) continue;
107             cs++;
108         }
109         if (cs>2) return 0;else return 1;
110     }
111
112     void make_ans()
113     {
114         memset(bj,0,sizeof(bj));
115         while (1)
116         {
117             bool WK=0;
118             for (llg i=1;i<=n;i++)
119                 if (!bj[i])
120                 {
121                     if (!pd(i)) continue;
122                     WK=1;
123                     ans++;
124                     DFS(i);
125                 }
126             if (!WK) break;
127         }
128     }
129 }G;
130
131 bool check(llg v1,llg v2)
132 {
133     llg x=v1+v2;
134     llg up=sqrt(x+1);
135     for (llg i=2;i<=up;i++)
136         if (x%i==0) return 0;
137     return 1;
138 }
139
140 void init()
141 {
142     cin>>n;
143     for (llg i=1;i<=n;i++) c[i]=getint();
144     for (llg i=1;i<=n;i++)
145     {
146         if (c[i]%2) G.link(0,i,2),cnt1++; else G.link(i,n+1,2),cnt2++;
147            if (c[i]%2==0) continue;
148         for (llg j=1;j<=n;j++)
149             if (i!=j && check(c[i],c[j]))
150                 G.link(i,j,1);
151     }
152     G.N=n+1;
153 }
154
155 int main()
156 {
157     yyj("flows");
158     init();
159     if (cnt1!=cnt2) {cout<<"Impossible"; return 0;}
160     llg flows=G.dinic();
161     if (flows!=n)  {cout<<"Impossible"; return 0;}
162     G.make_ans();
163     cout<<ans<<endl;
164     for (llg i=1;i<=ans;i++)
165     {
166         cout<<tot[i]<<" ";
167         for (llg j=1;j<=tot[i];j++) cout<<d[i][j]<<" ";
168         cout<<endl;
169     }
170     return 0;
171 }