#include <bits/stdc++.h>
using namespace std;
int prime[100001];
vector<int> kraw[201];
vector<int> cykle[201];
int tab[201];
int sko[201];
int odw[201];
int ile = 0;
int czy[201];
int mach(int x) {
  odw[x] = ile;
  for (vector<int>::iterator it = kraw[x].begin(); it != kraw[x].end(); it++) {
    if (sko[*it] == 0 && sko[x] != *it && odw[*it] != ile) {
      sko[*it] = x;
      return 1;
    }
  }
  for (vector<int>::iterator it = kraw[x].begin(); it != kraw[x].end(); it++) {
    if (odw[sko[*it]] != ile && sko[x] != *it && mach(sko[*it]) == 1) {
      sko[*it] = x;
      return 1;
    }
  }
  return 0;
}
int main() {
  int n;
  int wyn = 0;
  int m = 100000;
  prime[1] = 1;
  for (int i = 2; i <= m; i++) {
    if (prime[i] == 0)
      for (int j = 2 * i; j <= m; j += i) prime[j] = 1;
  }
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &tab[i]);
  }
  for (int i = 1; i <= n; i++)
    for (int j = i + 1; j <= n; j++) {
      if (prime[tab[i] + tab[j]] == 0) {
        kraw[i].push_back(j);
        kraw[j].push_back(i);
      }
    }
  for (int i = 1; i <= n; i++) {
    ile++;
    wyn += mach(i);
  }
  if (wyn < n)
    printf("Impossible");
  else {
    ile = 0;
    for (int i = 1; i <= n; i++) {
      if (czy[i] == 0) {
        ile++;
        int gdzie = i;
        while (czy[gdzie] == 0) {
          cykle[ile].push_back(gdzie);
          czy[gdzie] = 1;
          gdzie = sko[gdzie];
        }
      }
    }
    printf("%d\n", ile);
    for (int i = 1; i <= ile; i++) {
      printf("%d ", cykle[i].size());
      for (int j = 0; j < cykle[i].size(); j++) printf("%d ", cykle[i][j]);
      printf("\n");
    }
  }
}
