#include <bits/stdc++.h>
using namespace std;
const int MAXN = 202;
int c[MAXN][MAXN], f[MAXN][MAXN], in, a[MAXN], s, t;
int n;
bool mark[MAXN];
vector<int> ans[MAXN];
bool prime(int n) {
  for (int i = 2; i * i <= n; i++)
    if (n % i == 0) return false;
  return true;
}
void make_graph() {
  for (int i = 0; i < n; i++)
    for (int j = 0; j < n; j++)
      if (i != j && prime(a[i] + a[j]) && a[i] % 2 == 0) c[i][j] = 1;
  s = n, t = n + 1;
  for (int i = 0; i < n; i++)
    if (a[i] % 2 == 0) c[s][i] = 2;
  for (int i = 0; i < n; i++)
    if (a[i] % 2 == 1) c[i][t] = 2;
  n += 2;
}
int find_path(int n, int bn) {
  mark[n] = true;
  if (n == t) return bn;
  for (int i = 0; i < ::n; i++)
    if (!mark[i] && c[n][i] - f[n][i] > 0) {
      int val = find_path(i, min(bn, c[n][i] - f[n][i]));
      if (val > 0) {
        f[n][i] += val;
        f[i][n] -= val;
        return val;
      }
    }
  return 0;
}
int flow() {
  int F = 0;
  while (1) {
    fill(mark, mark + MAXN, 0);
    int val = find_path(s, 1e9);
    if (val == 0) return F;
    F += val;
  }
  return F;
}
void DFS(int n) {
  mark[n] = true;
  for (int i = 0; i < ::n; i++)
    if (!mark[i] && f[n][i]) DFS(i);
  ans[in].push_back(n);
}
int main() {
  cin >> n;
  for (int i = 0; i < n; i++) cin >> a[i];
  make_graph();
  int f = flow();
  n -= 2;
  if (f < n) {
    cout << "Impossible" << endl;
    return 0;
  }
  for (int i = 0; i < n; i++)
    if (!mark[i]) {
      DFS(i);
      in++;
    }
  for (int i = 0; i < n; i++)
    for (int j = 0; j < n; j++)
      if (::f[i][j]) ::f[j][i] = 1;
  cout << in << endl;
  for (int i = 0; i < in; i++, cout << endl) {
    cout << ans[i].size() << ' ';
    for (int j = 0; j < ans[i].size(); j++) cout << ans[i][j] + 1 << ' ';
  }
  return 0;
}
