#include <bits/stdc++.h>
using namespace std;
const int N = 405;
bool vis[N], p[20002];
int match[N], n, a[N];
vector<int> adj[N];
bool dfs(int x) {
  if (x == -1) return 0;
  int i, u;
  if (vis[x]) return 0;
  vis[x] = 1;
  for (i = 0; i < adj[x].size(); ++i) {
    u = adj[x][i];
    if (match[n + x] != u - n && (match[u] == -1 || dfs(match[u]))) {
      match[u] = x;
      return 1;
    }
  }
  return 0;
}
int main() {
  int u, i, j;
  for (i = 2; i < 20001; ++i)
    if (!p[i])
      for (j = i + i; j < 20001; j += i) p[j] = 1;
  cin >> n;
  for (i = 1; i <= n; ++i) scanf("%d", &a[i]);
  for (i = 1; i <= n; ++i)
    for (j = 1; j <= n; ++j)
      if (!p[a[i] + a[j]]) adj[i].push_back(n + j);
  memset(match, -1, sizeof(match));
  for (i = 1; i <= n; ++i) {
    memset(vis, 0, sizeof(vis));
    if (!dfs(i)) {
      printf("Impossible\n");
      return 0;
    }
  }
  memset(vis, 0, sizeof(vis));
  vector<vector<int> > ret;
  vector<int> R;
  for (i = 1; i <= n; ++i) {
    if (!vis[i]) {
      R.clear();
      R.push_back(i);
      u = match[i + n];
      vis[i] = 1;
      while (u != i) {
        R.push_back(u);
        vis[u] = 1;
        u = match[u + n];
      }
      ret.push_back(R);
    }
  }
  cout << ret.size() << endl;
  for (i = 0; i < ret.size(); ++i) {
    cout << ret[i].size() << " ";
    for (j = 0; j < ret[i].size(); ++j) printf("%d ", ret[i][j]);
    cout << endl;
  }
}
