#include <bits/stdc++.h>
using namespace std;
const int nmax = 2 * 200 + 42;
int n;
int a[nmax];
vector<int> adj[nmax];
bool prime(int x) {
  for (int i = 2; i * i <= x; i++)
    if (x % i == 0) return 0;
  return 1;
}
int parent[nmax];
int flow[nmax][nmax];
void dfs(int node, int par) {
  if (parent[node] != -1) return;
  parent[node] = par;
  for (auto k : adj[node])
    if (flow[node][k]) dfs(k, node);
}
set<int> matched[nmax];
vector<int> path[nmax];
bool been[nmax];
int pos = 0;
void make_path(int node) {
  if (been[node]) return;
  been[node] = 1;
  path[pos].push_back(node);
  for (auto k : adj[node]) make_path(k);
}
int main() {
  cin >> n;
  int even = 0, odd = 0;
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
    if (a[i] % 2 == 0)
      even++;
    else
      odd++;
  }
  if (even != odd) {
    cout << "Impossible" << endl;
    return 0;
  }
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= n; j++)
      if (a[i] % 2 == 1 && a[j] % 2 == 0 && prime(a[i] + a[j])) {
        adj[i].push_back(j + n);
        adj[j + n].push_back(i);
        flow[i][j + n] = 1;
      }
  for (int i = 1; i <= n; i++)
    if (a[i] % 2 == 1) {
      adj[0].push_back(i);
      flow[0][i] = 2;
    }
  for (int j = 1; j <= n; j++)
    if (a[j] % 2 == 0) {
      adj[n + j].push_back(2 * n + 1);
      flow[n + j][2 * n + 1] = 2;
    }
  int f = 0;
  while (1) {
    memset(parent, -1, sizeof(parent));
    dfs(0, 0);
    if (parent[2 * n + 1] == -1) break;
    f++;
    int node = 2 * n + 1, t = 0;
    while (node) {
      if (node != 2 * n + 1 && parent[node] != 0) {
        if (t % 2 == 0) {
          matched[node].erase(parent[node]);
        } else {
          matched[parent[node]].insert(node);
        }
      }
      t++;
      flow[parent[node]][node]--;
      flow[node][parent[node]]++;
      node = parent[node];
    }
  }
  if (f != n) {
    cout << "Impossible" << endl;
    return 0;
  }
  for (int i = 0; i <= 2 * n + 1; i++) adj[i].clear();
  for (int i = 1; i <= n; i++)
    if (a[i] % 2 == 1) {
      for (auto k : matched[i]) {
        adj[i].push_back(k - n);
        adj[k - n].push_back(i);
      }
    }
  memset(been, 0, sizeof(been));
  for (int i = 1; i <= n; i++)
    if (been[i] == 0) {
      pos++;
      make_path(i);
    }
  cout << pos << endl;
  for (int i = 1; i <= pos; i++) {
    cout << path[i].size();
    for (auto k : path[i]) cout << " " << k;
    cout << endl;
  }
  return 0;
}
