#include <bits/stdc++.h>
using namespace std;
const int N = 205;
vector<int> adj[N], mem[N];
int cap[N][N], edge[N][N], visit[N], p[N], n, source, sink, a[N], cnt, max_flow;
int is_prime(int a) {
  for (int i = 2; i * i <= a; i++)
    if (a % i == 0) return 0;
  return 1;
}
void add(int u, int v, int _cap) {
  adj[u].push_back(v);
  adj[v].push_back(u);
  cap[u][v] = _cap;
  edge[u][v] = 1;
}
int bfs() {
  memset(visit, 0, sizeof visit);
  queue<int> q;
  q.push(source);
  visit[source] = 1;
  while (!q.empty()) {
    int u = q.front();
    q.pop();
    if (u == sink) return 1;
    for (int v : adj[u])
      if (cap[u][v] && !visit[v]) {
        visit[v] = 1;
        p[v] = u;
        q.push(v);
      }
  }
  return 0;
}
void dfs(int u) {
  visit[u] = 1;
  mem[cnt].push_back(u);
  for (int v : adj[u])
    if (!visit[v]) dfs(v);
}
int main() {
  cin >> n;
  source = 0;
  sink = n + 1;
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
    if (a[i] % 2)
      add(source, i, 2);
    else
      add(i, sink, 2);
  }
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= n; j++)
      if (a[i] % 2 && a[j] % 2 == 0 && is_prime(a[i] + a[j])) add(i, j, 1);
  while (bfs()) {
    int flow_path = 1e9;
    for (int v = sink; v != source; v = p[v])
      flow_path = min(flow_path, cap[p[v]][v]);
    max_flow += flow_path;
    for (int v = sink; v != source; v = p[v]) {
      cap[p[v]][v] -= flow_path;
      cap[v][p[v]] += flow_path;
    }
  }
  if (max_flow != n) {
    cout << "Impossible";
    return 0;
  }
  for (int i = 1; i <= n; i++) adj[i].clear();
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= n; j++)
      if (edge[i][j] && !cap[i][j]) {
        adj[i].push_back(j);
        adj[j].push_back(i);
      }
  memset(visit, 0, sizeof visit);
  for (int i = 1; i <= n; i++) {
    if (!visit[i]) {
      cnt++;
      dfs(i);
    }
  }
  cout << cnt << '\n';
  for (int i = 1; i <= cnt; i++) {
    cout << mem[i].size() << ' ';
    for (int j : mem[i]) cout << j << ' ';
    cout << '\n';
  }
}
