#include <bits/stdc++.h>
using namespace std;
const int MAXN = 210, MAXA = 20010;
void kill(bool b) {
  if (b) {
    puts("Impossible");
    exit(0);
  }
}
int N, A[MAXN];
bool isprime[MAXA];
int cap[MAXN][MAXN];
vector<int> adj[MAXN];
vector<vector<int> > ans;
bool vis[MAXN];
void add(int x, int y, int v) {
  adj[x].push_back(y);
  adj[y].push_back(x);
  cap[x][y] = v;
}
bool dfs(int s, int t) {
  if (s == t) {
    return true;
  }
  if (vis[s]) {
    return false;
  }
  vis[s] = true;
  for (__typeof((adj[s]).begin()) it = (adj[s]).begin(); it != (adj[s]).end();
       it++) {
    int v = *it;
    if (cap[s][v] && dfs(v, t)) {
      cap[s][v]--;
      cap[v][s]++;
      return true;
    }
  }
  return false;
}
int main() {
  if (fopen("input.txt", "r")) {
    freopen("input.txt", "r", stdin);
  }
  ios::sync_with_stdio(false);
  cin >> N;
  int nodd = 0, neven = 0;
  for (int i = 1; i <= N; i++) {
    cin >> A[i];
    if (A[i] % 2) {
      add(i, N + 1, 2);
      nodd++;
    } else {
      add(0, i, 2);
      neven++;
    }
  }
  kill(nodd != neven);
  memset((isprime), (true), sizeof(isprime));
  for (int i = 2; i < MAXA; i++) {
    for (int j = 2; j * j <= i; j++) {
      if (i % j == 0) {
        isprime[i] = false;
        break;
      }
    }
  }
  for (int i = 1; i <= N; i++) {
    for (int j = i + 1; j <= N; j++) {
      if (!isprime[A[i] + A[j]]) {
        continue;
      }
      int a = i, b = j;
      if (A[i] % 2) {
        swap(a, b);
      }
      add(a, b, 1);
    }
  }
  int flow = 0;
  while (dfs(0, N + 1)) {
    flow++;
    memset((vis), (false), sizeof(vis));
  }
  kill(flow != N);
  for (int i = 1; i <= N; i++) {
    adj[i].clear();
  }
  for (int i = 1; i <= N; i++) {
    for (int j = i + 1; j <= N; j++) {
      if (!isprime[A[i] + A[j]]) {
        continue;
      }
      int a = i, b = j;
      if (A[i] % 2) {
        swap(a, b);
      }
      if (cap[b][a] == 1) {
        adj[a].push_back(b);
        adj[b].push_back(a);
      }
    }
  }
  for (int i = 1; i <= N; i++) {
    assert(adj[i].size() == 2);
  }
  memset((vis), (false), sizeof(vis));
  for (int i = 1; i <= N; i++) {
    if (!vis[i]) {
      int x = i;
      vector<int> cyc;
      while (true) {
        vis[x] = true;
        cyc.push_back(x);
        bool found = false;
        for (__typeof((adj[x]).begin()) it = (adj[x]).begin();
             it != (adj[x]).end(); it++) {
          int t = *it;
          if (!vis[t]) {
            x = t;
            found = true;
            break;
          }
        }
        if (!found) {
          break;
        }
      }
      ans.push_back(cyc);
    }
  }
  cout << ans.size() << '\n';
  for (__typeof((ans).begin()) it = (ans).begin(); it != (ans).end(); it++) {
    vector<int> &v = *it;
    cout << v.size() << ' ';
    for (__typeof((v).begin()) jt = (v).begin(); jt != (v).end(); jt++) {
      cout << *jt << ' ';
    }
    cout << '\n';
  }
}
