#include <bits/stdc++.h>
using namespace std;
const int INF = 1 << 30;
struct Dinic {
  struct Edge {
    int to, flow;
    Edge(int a, int b) : to(a), flow(b) {}
  };
  vector<vector<int>> G;
  vector<int> dis;
  vector<Edge> e;
  int n, s, t;
  Dinic(int sz) : n(sz), G(sz + 1), dis(sz + 1) {}
  void add(int u, int v, int f) {
    G[u].emplace_back(e.size());
    e.emplace_back(v, f);
    G[v].emplace_back(e.size());
    e.emplace_back(u, 0);
  }
  bool bfs() {
    fill(begin(dis), end(dis), -1);
    queue<int> que;
    que.emplace(s);
    dis[s] = 0;
    while (que.size()) {
      int x = que.front();
      que.pop();
      for (int id : G[x]) {
        int y = e[id].to;
        if (e[id].flow > 0 && dis[y] == -1) {
          dis[y] = dis[x] + 1;
          que.emplace(y);
        }
      }
    }
    return dis[t] != -1;
  }
  int dfs(int x, int f = INF) {
    if (x == t || f == 0) return f;
    int a, flow = 0;
    for (int id : G[x]) {
      int y = e[id].to;
      if (e[id].flow > 0 && dis[y] == dis[x] + 1) {
        a = dfs(y, min(f, e[id].flow));
        e[id ^ 1].flow += a;
        e[id].flow -= a;
        flow += a;
        f -= a;
        if (!f) return flow;
      }
    }
    return flow;
  }
  int solve(int _s, int _t) {
    s = _s;
    t = _t;
    int df, flow = 0;
    while (bfs()) {
      while (df = dfs(s)) flow += df;
    }
    return flow;
  }
};
vector<bool> isprime(int sz) {
  vector<bool> ret(sz + 1, true);
  ret[0] = ret[1] = false;
  for (int i = 2; i <= sz; i++) {
    if (ret[i]) {
      for (int j = i + i; j <= sz; j += i) {
        ret[j] = false;
      }
    }
  }
  return ret;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  int N;
  cin >> N;
  if (N & 1) {
    cout << "Impossible\n";
    return 0;
  }
  vector<int> arr(N + 1);
  auto is = isprime(20000);
  for (int i = 1; i <= N; i++) {
    cin >> arr[i];
  }
  Dinic loli(N + 1);
  for (int i = 1; i <= N; i++) {
    if (arr[i] & 1) {
      loli.add(0, i, 2);
    } else {
      loli.add(i, N + 1, 2);
    }
    for (int j = 1; j <= N; j++) {
      if (is[arr[i] + arr[j]]) {
        if (arr[i] % 2 == 1 && arr[j] % 2 == 0) loli.add(i, j, 1);
      }
    }
  }
  if (loli.solve(0, N + 1) != N) {
    cout << "Impossible\n";
    return 0;
  }
  vector<vector<int>> G(N + 1);
  for (int i = 1; i <= N; i++) {
    for (int id : loli.G[i]) {
      if (arr[i] % 2 == 1 && loli.e[id].flow == 0) {
        G[i].push_back(loli.e[id].to);
        G[loli.e[id].to].push_back(i);
      }
    }
  }
  vector<vector<int>> ans;
  vector<bool> vis(N + 1);
  vector<int> stk;
  function<void(int)> dfs = [&](int x) {
    vis[x] = true;
    stk.push_back(x);
    for (int y : G[x]) {
      if (!vis[y]) dfs(y);
    }
  };
  for (int i = 1; i <= N; i++) {
    if (!vis[i]) {
      stk.clear();
      dfs(i);
      ans.push_back(stk);
    }
  }
  cout << ans.size() << '\n';
  for (auto it : ans) {
    cout << it.size();
    for (int x : it) {
      cout << ' ' << x;
    }
    cout << '\n';
  }
  return 0;
}
