#include <bits/stdc++.h>
using namespace std;
int n;
bool pr[100100];
int a[100100];
vector<int> p[100100];
struct ed {
  int first, to, ca, fl;
};
int k;
ed edg[100100];
int dist[100100];
bool bfs() {
  queue<int> q;
  for (int i = 0; i <= n + 1; i++) {
    dist[i] = 1e9;
  }
  dist[0] = 0;
  q.push(0);
  while (!q.empty()) {
    int t = q.front();
    q.pop();
    for (int i = 0; i < p[t].size(); i++) {
      int in = p[t][i];
      if (dist[edg[in].to] > dist[t] + 1 && edg[in].fl < edg[in].ca) {
        dist[edg[in].to] = dist[t] + 1;
        q.push(edg[in].to);
      }
    }
  }
  return dist[n + 1] < 1e8;
}
int it[100100];
int dfs(int x, int fl) {
  if (!fl) return 0;
  if (x == n + 1) return fl;
  for (; it[x] < p[x].size(); it[x]++) {
    int in = p[x][it[x]];
    if (dist[edg[in].to] != dist[x] + 1) continue;
    int t = dfs(edg[in].to, min(fl, edg[in].ca - edg[in].fl));
    if (t) {
      edg[in].fl += t;
      edg[in ^ 1].fl -= t;
      return t;
    }
  }
  return 0;
}
int maxflow() {
  int r = 0;
  while (bfs()) {
    memset(it, 0, sizeof it);
    int y;
    while (y = dfs(0, 1e9)) r += y;
  }
  return r;
}
bool v[100100];
vector<vector<int> > res;
void print(int x) {
  if (x == 0) return;
  if (x == n + 1) return;
  if (v[x]) return;
  v[x] = 1;
  res.back().push_back(x);
  for (int i = 0; i < p[x].size(); i++) {
    if (edg[p[x][i]].fl) {
      print(edg[p[x][i]].to);
    }
  }
}
int main() {
  ios::sync_with_stdio(0);
  for (int i = 2; i < 100100; i++) {
    if (!pr[i]) {
      for (int j = i * 2; j < 100100; j += i) pr[j] = 1;
    }
  }
  cin >> n;
  for (int i = 1; i <= n; i++) cin >> a[i];
  for (int i = 1; i <= n; i++) {
    for (int j = i + 1; j <= n; j++) {
      if (pr[a[i] + a[j]]) continue;
      if (a[i] % 2 != 0) {
        p[i].push_back(k);
        edg[k].first = i;
        edg[k].to = j;
        edg[k].ca = 1;
        edg[k].fl = 0;
        k++;
        p[j].push_back(k);
        edg[k].first = j;
        edg[k].to = i;
        edg[k].ca = 0;
        edg[k].fl = 0;
        k++;
      } else {
        p[j].push_back(k);
        edg[k].first = j;
        edg[k].to = i;
        edg[k].ca = 1;
        edg[k].fl = 0;
        k++;
        p[i].push_back(k);
        edg[k].first = i;
        edg[k].to = j;
        edg[k].ca = 0;
        edg[k].fl = 0;
        k++;
      }
    }
  }
  int d = 0;
  for (int i = 1; i <= n; i++) {
    if (a[i] % 2 != 0) {
      d++;
      p[0].push_back(k);
      edg[k].first = 0;
      edg[k].to = i;
      edg[k].ca = 2;
      edg[k].fl = 0;
      k++;
      p[i].push_back(k);
      edg[k].first = i;
      edg[k].to = 0;
      edg[k].ca = 0;
      edg[k].fl = 0;
      k++;
    } else {
      p[i].push_back(k);
      edg[k].first = i;
      edg[k].to = n + 1;
      edg[k].ca = 2;
      edg[k].fl = 0;
      k++;
      p[n + 1].push_back(k);
      edg[k].first = n + 1;
      edg[k].to = i;
      edg[k].ca = 0;
      edg[k].fl = 0;
      k++;
    }
  }
  int f = maxflow();
  if (f != n || d != n / 2) {
    cout << "Impossible" << endl;
    return 0;
  }
  for (int i = 1; i <= n; i++) {
    if (!v[i]) {
      res.push_back(vector<int>());
      print(i);
    }
  }
  cout << res.size() << endl;
  for (int i = 0; i < res.size(); i++) {
    cout << res[i].size();
    for (int j = 0; j < res[i].size(); j++) {
      cout << " " << res[i][j];
    }
    cout << "\n";
  }
  return 0;
}
