#include <bits/stdc++.h>
using namespace std;
const int mxn = 222;
int a[mxn], dist[mxn][mxn], used[mxn], r[mxn][mxn], ring[mxn][mxn], cntgs[mxn];
int n, cntring, s, t;
inline bool isp(int x) {
  for (int i = 2; i * i <= x; ++i)
    if (x % i == 0) return 0;
  return 1;
}
inline bool find(int x) {
  if (x == t) return 1;
  if (used[x]) return 0;
  used[x] = 1;
  for (int i = 1; i <= t; ++i)
    if (dist[x][i] and find(i)) {
      --dist[x][i];
      ++dist[i][x];
      return 1;
    }
  return 0;
}
inline void dfs(int x) {
  if (used[x]) return;
  used[x] = 1;
  ring[cntring][cntgs[cntring]++] = x;
  for (int i = 1; i <= 200; ++i)
    if (r[x][i]) dfs(i);
}
int main() {
  cin >> n;
  s = 0, t = 201;
  for (int i = 1; i <= n; ++i) {
    cin >> a[i];
    if (a[i] & 1)
      dist[s][i] = 2;
    else
      dist[i][t] = 2;
  }
  for (int i = 1; i <= n; ++i)
    for (int j = 1; j <= n; ++j)
      if (a[i] % 2 == 1 and a[j] % 2 == 0 and isp(a[i] + a[j])) dist[i][j] = 1;
  int tms = 0;
  while (find(s)) ++tms, memset(used, 0, sizeof(used));
  if (tms < n) return puts("Impossible") * 0;
  for (int i = 1; i <= n; ++i)
    for (int j = 1; j <= n; ++j)
      if (a[i] % 2 == 1 and a[j] % 2 == 0 and isp(a[i] + a[j]) and !dist[i][j])
        r[i][j] = r[j][i] = 1;
  memset(used, 0, sizeof(used));
  for (int i = 1; i <= n; ++i)
    if (!used[i]) dfs(i), ++cntring;
  cout << cntring << endl;
  for (int i = 0; i < cntring; ++i) {
    cout << cntgs[i] << ' ';
    for (int j = 0; j < cntgs[i]; ++j) cout << ring[i][j] << ' ';
    cout << '\n';
  }
}
