#include <bits/stdc++.h>
using namespace std;
bool p[300005], vis[300005];
int n, a[405], c[405][405], source, sink, f[405][405], d[405], num;
vector<int> ans[405];
vector<int> graph[405];
queue<int> q;
bool bfs() {
  for (int i = 1; i <= 2 * n + 2; i++) d[i] = 0;
  d[source] = 1;
  q.push(source);
  while (!q.empty()) {
    int u = q.front();
    q.pop();
    for (int i = 0; i < graph[u].size(); i++) {
      int v = graph[u][i];
      if (!d[v] && f[u][v] < c[u][v]) {
        d[v] = u;
        q.push(v);
      }
    }
  }
  return (d[sink]);
}
void augment() {
  int u = sink, v, a = 1e9;
  while (u != source) {
    v = d[u];
    a = min(a, c[v][u] - f[v][u]);
    u = v;
  }
  u = sink;
  while (u != source) {
    v = d[u];
    f[v][u] += a;
    f[u][v] -= a;
    u = v;
  }
}
void dfs(int u) {
  vis[u] = 1;
  ans[num].push_back(u);
  for (int i = 0; i < graph[u].size(); i++) {
    int v = graph[u][i];
    if (!vis[v] && abs(f[u][v]) == 1) dfs(v);
  }
}
int main() {
  cin.tie(0), ios::sync_with_stdio(0);
  for (int i = 2; i <= 20000; i++) p[i] = 1;
  for (int i = 2; i <= 20000; i++) {
    if (p[i]) {
      for (int j = 2 * i; j <= 20000; j += i) p[j] = 0;
    }
  }
  cin >> n;
  for (int i = 1; i <= n; i++) cin >> a[i];
  source = 2 * n + 1;
  sink = 2 * n + 2;
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= n; j++) {
      if (a[i] % 2 == 0 && p[a[i] + a[j]]) {
        c[i][j] = 1;
        graph[i].push_back(j);
        graph[j].push_back(i);
      }
    }
    if (a[i] % 2 == 0 && graph[i].size() < 2) {
      cout << "Impossible\n";
      exit(0);
    }
  }
  for (int i = 1; i <= n; i++) {
    if (a[i] % 2 == 0) {
      graph[source].push_back(i);
      graph[i].push_back(source);
      c[source][i] = 2;
    }
  }
  for (int i = 1; i <= n; i++) {
    if (a[i] % 2 != 0) {
      graph[sink].push_back(i);
      graph[i].push_back(sink);
      c[i][sink] = 2;
    }
  }
  while (bfs()) augment();
  int sum = 0;
  for (int i = 0; i < graph[source].size(); i++) {
    sum += f[source][graph[source][i]];
    if (f[source][graph[source][i]] != 2) {
      cout << "Impossible\n";
      exit(0);
    }
  }
  if (sum != n) {
    cout << "Impossible\n";
    exit(0);
  }
  for (int i = 1; i <= n; i++) {
    if (a[i] % 2 == 0 && vis[i] == 0) {
      dfs(i);
      num++;
    }
  }
  cout << num << "\n";
  for (int i = 0; i < num; i++) {
    cout << ans[i].size() << " ";
    for (int j = 0; j < ans[i].size(); j++) cout << ans[i][j] << " ";
    cout << "\n";
  }
}
