#include <bits/stdc++.h>
using namespace std;
bool is_prime(int a) {
  for (int i = 2; i * i <= a; i++) {
    if (a % i == 0) return 0;
  }
  return 1;
}
int n;
bool kuhn(int s, vector<vector<int>> &g, vector<int> &vis, vector<int> &now,
          vector<int> &p) {
  vis[s] = 1;
  for (int to : g[s]) {
    if (now[to - n] == s + n || p[to - n] == s + n) continue;
    if (p[to] == -1) {
      p[to] = s;
      p[s] = to;
      return true;
    }
    if (vis[p[to]]) continue;
    now[s] = to;
    if (kuhn(p[to], g, vis, now, p)) {
      p[to] = s;
      p[s] = to;
      return true;
    }
  }
  return false;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin >> n;
  vector<int> a(n);
  for (int i = 0; i < n; i++) cin >> a[i];
  vector<vector<int>> g(n + n);
  for (int i = 0; i < n; i++)
    for (int j = i + 1; j < n; j++) {
      if (is_prime(a[i] + a[j])) {
        g[i].push_back(j + n);
        g[j].push_back(i + n);
      }
    }
  vector<int> p(n + n, -1);
  vector<int> vis(n + n), now(n + n, -1);
  for (int i = 0; i < n; i++) {
    fill(vis.begin(), vis.end(), 0);
    fill(now.begin(), now.end(), -1);
    kuhn(i, g, vis, now, p);
  }
  for (int i = 0; i < p.size(); i++)
    if (p[i] == -1) {
      cout << "Impossible";
      return 0;
    }
  vector<vector<int>> ans;
  fill(vis.begin(), vis.end(), 0);
  for (int i = 0; i < p.size(); i++) {
    if ((i < n && vis[i]) || (i >= n && vis[i - n])) continue;
    int cur = i, q = p[i] - n;
    vis[cur] = 1;
    ans.push_back(vector<int>({cur}));
    while (q != cur) {
      vis[q] = 1;
      ans.back().push_back(q);
      q = p[q] - n;
    }
  }
  cout << ans.size() << endl;
  for (int i = 0; i < ans.size(); i++) {
    cout << ans[i].size() << " ";
    for (int j = 0; j < ans[i].size(); j++) cout << ans[i][j] + 1 << " ";
    cout << "\n";
  }
}
