#include <bits/stdc++.h>
using namespace std;
int n, a[220], odd = 0, even = 0, seen[220] = {};
vector<int> temp, graph[220];
const int INF = 2000000000;
struct Edge {
  int from, to, cap, flow, index;
  Edge(int from, int to, int cap, int flow, int index)
      : from(from), to(to), cap(cap), flow(flow), index(index) {}
};
struct Dinic {
  int N;
  vector<vector<Edge> > G;
  vector<Edge *> dad;
  vector<int> Q;
  Dinic(int N) : N(N), G(N), dad(N), Q(N) {}
  void AddEdge(int from, int to, int cap) {
    G[from].push_back(Edge(from, to, cap, 0, G[to].size()));
    if (from == to) G[from].back().index++;
    G[to].push_back(Edge(to, from, 0, 0, G[from].size() - 1));
  }
  long long BlockingFlow(int s, int t) {
    fill(dad.begin(), dad.end(), (Edge *)NULL);
    dad[s] = &G[0][0] - 1;
    int head = 0, tail = 0;
    Q[tail++] = s;
    while (head < tail) {
      int x = Q[head++];
      for (int i = 0; i < G[x].size(); i++) {
        Edge &e = G[x][i];
        if (!dad[e.to] && e.cap - e.flow > 0) {
          dad[e.to] = &G[x][i];
          Q[tail++] = e.to;
        }
      }
    }
    if (!dad[t]) return 0;
    long long totflow = 0;
    for (int i = 0; i < G[t].size(); i++) {
      Edge *start = &G[G[t][i].to][G[t][i].index];
      int amt = INF;
      for (Edge *e = start; amt && e != dad[s]; e = dad[e->from]) {
        if (!e) {
          amt = 0;
          break;
        }
        amt = min(amt, e->cap - e->flow);
      }
      if (amt == 0) continue;
      for (Edge *e = start; amt && e != dad[s]; e = dad[e->from]) {
        e->flow += amt;
        G[e->to][e->index].flow -= amt;
      }
      totflow += amt;
    }
    return totflow;
  }
  long long GetMaxFlow(int s, int t) {
    long long totflow = 0;
    while (long long flow = BlockingFlow(s, t)) totflow += flow;
    return totflow;
  }
};
bool isPrime(int num) {
  for (int i = 2; i * i <= num; i++) {
    if (num % i == 0) {
      return false;
    }
  }
  return true;
}
void dfs(int node) {
  seen[node] = true;
  temp.push_back(node);
  for (auto next : graph[node]) {
    if (not seen[next]) {
      dfs(next);
    }
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    if (a[i] & 1) {
      odd++;
    } else {
      even++;
    }
  }
  Dinic G(n + 2);
  for (int i = 0; i < n; i++) {
    if (a[i] & 1) {
      G.AddEdge(0, i + 1, 2);
      for (int j = 0; j < n; j++) {
        if (isPrime(a[i] + a[j])) {
          G.AddEdge(i + 1, j + 1, 1);
        }
      }
    } else {
      G.AddEdge(i + 1, n + 1, 2);
    }
  }
  int flow = G.GetMaxFlow(0, n + 1);
  if (flow != 2 * odd or even != odd) {
    cout << "Impossible\n";
    return 0;
  }
  vector<vector<int> > ans;
  for (int i = 0; i < n; i++) {
    if (a[i] & 1) {
      int node = i + 1;
      for (auto edge : G.G[node]) {
        if (edge.flow == 1) {
          graph[node - 1].push_back(edge.to - 1);
          graph[edge.to - 1].push_back(node - 1);
        }
      }
    }
  }
  for (int i = 0; i < n; i++) {
    if (not seen[i]) {
      temp.clear();
      dfs(i);
      ans.push_back(temp);
    }
  }
  cout << ans.size() << "\n";
  for (auto el : ans) {
    cout << el.size() << " ";
    for (int i : el) {
      cout << i + 1 << " ";
    }
    cout << "\n";
  }
}
