#include<cstdio>

#include<cstring>

#include<string>

#include<cmath>

#include<vector>

#include<queue>

#include<algorithm>

using namespace std;

const int maxn =  + ;

const int INF = 0x7FFFFFFF;

struct Edge

{

    int from, to, cap, flow;

    Edge(int u, int v, int c, int f) :from(u), to(v), cap(c), flow(f){}

};

vector<Edge>edges;

vector<int>G[maxn];

bool vis[maxn];

int d[maxn];

int cur[maxn];

int n, m, s, t;

int num[maxn];

vector<int>g[maxn];

vector<int> ans[maxn];

bool f[maxn];

int block;

void init()

{

    for (int i = ; i < maxn; i++) G[i].clear();

    edges.clear();

}

void AddEdge(int from, int to, int cap)

{

    edges.push_back(Edge(from, to, cap, ));

    edges.push_back(Edge(to, from, , ));

    int w = edges.size();

    G[from].push_back(w - );

    G[to].push_back(w - );

}

bool BFS()

{

    memset(vis, , sizeof(vis));

    queue<int>Q;

    Q.push(s);

    d[s] = ;

    vis[s] = ;

    while (!Q.empty())

    {

        int x = Q.front();

        Q.pop();

        for (int i = ; i<G[x].size(); i++)

        {

            Edge e = edges[G[x][i]];

            if (!vis[e.to] && e.cap>e.flow)

            {

                vis[e.to] = ;

                d[e.to] = d[x] + ;

                Q.push(e.to);

            }

        }

    }

    return vis[t];

}

int DFS(int x, int a)

{

    if (x == t || a == )

        return a;

    int flow = , f;

    for (int &i = cur[x]; i<G[x].size(); i++)

    {

        Edge e = edges[G[x][i]];

        if (d[x]+ == d[e.to]&&(f=DFS(e.to,min(a,e.cap-e.flow)))>)

        {

            edges[G[x][i]].flow+=f;

            edges[G[x][i] ^ ].flow-=f;

            flow+=f;

            a-=f;

            if(a==) break;

        }

    }

    if(!flow) d[x] = -;

    return flow;

}

int dinic(int s, int t)

{

    int flow = ;

    while (BFS())

    {

        memset(cur, , sizeof(cur));

        flow += DFS(s, INF);

    }

    return flow;

}

bool prime(int x)

{

    for(int i=;i*i<=x;i++)

        if(x%i==) return ;

    return ;

}

void Find(int now)

{

    f[now]=;

    ans[block].push_back(now);

    for(int i=;i<g[now].size();i++)

    {

        if(f[g[now][i]]) continue;

        Find(g[now][i]);

    }

}

int main()

{

    while(~scanf("%d",&n))

    {

        for(int i=;i<=n;i++) scanf("%d",&num[i]);

        init();

        s=;t=n+; int e1=,e2=;

        int flag=;

        for(int i=;i<=n;i++)

        {

            if(num[i]%==) { e1++; AddEdge(s,i,); }

            else { e2++; AddEdge(i,t,); }

        }

        if(e1!=e2) flag=;

        else

        {

            for(int i=;i<=n;i++)

                for(int j=;j<=n;j++)

                    if(num[i]%==&&num[j]%==&&prime(num[i]+num[j]))

                        AddEdge(i,j,);

            int Flow=dinic(s,t);

            if(Flow!=*e1) flag=;

        }

        if(flag==) printf("Impossible\n");

        else

        {

            block=; memset(f,,sizeof f);

            for(int i=;i<maxn;i++) { g[i].clear(); ans[i].clear(); }

            for(int i=;i<edges.size();i=i+)

            {

                if(edges[i].flow==)

                {

                    int u=edges[i].from;

                    int v=edges[i].to;

                    g[u].push_back(v);

                    g[v].push_back(u);

                }

            }

            for(int i=;i<=n;i++)

            {

                if(f[i]) continue;

                Find(i); block++;

            }

            printf("%d\n",block);

            for(int i=;i<block;i++)

            {

                printf("%d ",ans[i].size());

                for(int j=;j<ans[i].size();j++)

                    printf("%d ",ans[i][j]);

                printf("\n");

            }

        }

    }

    return ;

}