#include <bits/stdc++.h>
using namespace std;
int n;
vector<int> A, B, aa, bb;
int q[555][555];
int in[555][555];
int second, T;
int f[555];
void er() {
  puts("Impossible");
  exit(0);
}
bool prime(int x) {
  for (int i = 2; i < x; i++)
    if (x % i == 0) return 0;
  return 1;
}
void ae(int x, int y, int f) {
  q[x][y] += f;
  in[x][y] += f;
}
void rec(int x) {
  for (int i = 0; i <= T; i++)
    if (q[x][i] > 0 && f[i] == -1) {
      f[i] = x;
      rec(i);
    }
}
int main() {
  cin >> n;
  for (int i = 0; i < n; i++) {
    int x;
    scanf("%d", &x);
    if (x % 2) {
      A.push_back(x);
      aa.push_back(i);
    } else {
      B.push_back(x);
      bb.push_back(i);
    }
  }
  if (A.size() != B.size()) er();
  second = 0;
  T = 1 + A.size() + B.size();
  for (int i = 0; i < A.size(); i++) ae(second, i + 1, 2);
  for (int i = 0; i < A.size(); i++)
    for (int j = 0; j < B.size(); j++)
      if (prime(A[i] + B[j])) ae(i + 1, 1 + A.size() + j, 1);
  for (int i = 0; i < B.size(); i++) ae(1 + A.size() + i, T, 2);
  int fl = 0;
  for (;;) {
    for (int i = 0; i <= T; i++) f[i] = -1;
    rec(second);
    if (f[T] == -1) break;
    fl++;
    int x = T;
    while (x != second) {
      q[f[x]][x]--;
      q[x][f[x]]++;
      x = f[x];
    }
  }
  if (fl != A.size() * 2) er();
  vector<vector<int> > ans;
  for (int i = 0; i < A.size(); i++) f[i] = 0;
  for (int i = 0; i < A.size(); i++)
    if (!f[i]) {
      vector<int> t;
      int x = i;
      int pr = -1;
      for (;;) {
        f[x] = 1;
        t.push_back(aa[x]);
        int g = -1;
        for (int j = 0; j < B.size(); j++)
          if (q[x + 1][1 + A.size() + j] < in[x + 1][1 + A.size() + j] &&
              j != pr)
            g = j;
        t.push_back(bb[g]);
        pr = x;
        for (int j = 0; j < A.size(); j++)
          if (q[1 + j][1 + A.size() + g] < in[1 + j][1 + A.size() + g] &&
              j != pr)
            x = j;
        pr = g;
        if (x == i) break;
      }
      ans.push_back(t);
    }
  cout << ans.size() << endl;
  for (int i = 0; i < ans.size(); i++) {
    cout << ans[i].size();
    for (int j = 0; j < ans[i].size(); j++) printf(" %d", ans[i][j] + 1);
    puts("");
  }
  return 0;
}
