#include <bits/stdc++.h>
using namespace std;
void fast() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
}
const int INF = 1e9 + 9;
const int N = 210;
const int M = 1e5 + 5;
vector<vector<int>> ans(N);
vector<vector<int>> capacity(N, vector<int>(N, 0));
vector<int> v(N);
vector<bool> p(M, 1);
vector<bool> vis(N, 0);
int n;
int dfs(int a, int flow) {
  if (a == n + 1 || flow == 0) return flow;
  int ans = 0;
  vis[a] = 1;
  for (int i = 0; i <= n + 1; i++) {
    if (vis[i] || capacity[a][i] == 0) continue;
    int temp = dfs(i, min(flow, capacity[a][i]));
    if (temp == 0) continue;
    capacity[a][i] -= temp;
    capacity[i][a] += temp;
    return temp;
  }
  return 0;
}
int get() {
  int ans = 0;
  while (1) {
    int newFlow = dfs(0, INF);
    if (newFlow == 0) break;
    ans += newFlow;
    for (int i = 0; i <= n + 1; i++) vis[i] = 0;
  }
  return ans;
}
void dfs2(int a, int idx) {
  vis[a] = 1;
  ans[idx].push_back(a);
  for (int i = 1; i <= n; i++) {
    if (vis[i]) continue;
    if (v[a] % 2 == 0 && v[i] % 2 == 1 && capacity[a][i] > 0) {
      dfs2(i, idx);
      break;
    }
    if (v[a] % 2 == 1 && v[i] % 2 == 0 && capacity[i][a] > 0) {
      dfs2(i, idx);
      break;
    }
  }
}
void solve() {
  for (int i = 2; i * i < M; i++)
    if (p[i])
      for (int j = i * i; j < M; j += i) p[j] = 0;
  int cnt = 0;
  for (int i = 1; i <= n; i++) {
    if (v[i] & 1) {
      cnt++;
      capacity[0][i] = 2;
    } else {
      cnt--;
      capacity[i][n + 1] = 2;
    }
  }
  if (cnt != 0) {
    cout << "Impossible\n";
    return;
  }
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= n; j++) {
      if (v[i] % 2 == 1 && v[j] % 2 == 0 && p[v[i] + v[j]]) capacity[i][j] = 1;
    }
  int flow = get();
  if (flow != n) {
    cout << "Impossible\n";
    return;
  }
  for (int i = 0; i <= n + 1; i++) vis[i] = 0;
  int idx = 0;
  for (int i = 1; i <= n; i++) {
    if (vis[i]) continue;
    dfs2(i, idx);
    idx++;
  }
  cout << idx << "\n";
  for (int i = 0; i < idx; i++) {
    cout << int(ans[i].size()) << ' ';
    for (int j : ans[i]) cout << j << ' ';
    cout << "\n";
  }
}
int main() {
  fast();
  cin >> n;
  for (int i = 1; i <= n; i++) cin >> v[i];
  solve();
}
