#include <bits/stdc++.h>
using namespace std;
const int nmax = 205;
int n, v[nmax], c[nmax][nmax], f[nmax][nmax], t[nmax], a, b, cnt;
bool viz[nmax];
vector<int> G[nmax], ans[nmax];
bool bfs() {
  memset(viz, 0, sizeof viz);
  queue<int> coada;
  coada.push(0);
  viz[0] = true;
  while (!coada.empty()) {
    int nod = coada.front();
    coada.pop();
    if (nod == 201) continue;
    for (auto it : G[nod]) {
      if (viz[it] == true || f[nod][it] == c[nod][it]) continue;
      coada.push(it);
      viz[it] = true;
      t[it] = nod;
    }
  }
  return viz[201];
}
void Find(int nod) {
  viz[nod] = true;
  ans[cnt].push_back(nod);
  for (auto it : G[nod]) {
    if (it == 0 || it == 201 || viz[it] == true || abs(f[nod][it]) != 1)
      continue;
    Find(it);
    return;
  }
}
bool isPrim(int x) {
  if (x == 2) return true;
  if (x % 2 == 0) return false;
  for (int i = 3; i * i <= x; i += 2) {
    if (x % i == 0) {
      return false;
    }
  }
  return true;
}
int main() {
  cin >> n;
  for (int i = 1; i <= n; ++i) {
    cin >> v[i];
    if (v[i] % 2 == 0) {
      ++a;
      for (int j = i - 1; j >= 1; --j) {
        if (v[j] % 2 == 1 && isPrim(v[j] + v[i])) {
          c[i][j] = 1;
          G[i].push_back(j);
          G[j].push_back(i);
        }
      }
      c[0][i] = 2;
      G[0].push_back(i);
      G[i].push_back(0);
    } else {
      ++b;
      for (int j = i - 1; j >= 1; --j) {
        if (v[j] % 2 == 0 && isPrim(v[j] + v[i])) {
          c[j][i] = 1;
          G[i].push_back(j);
          G[j].push_back(i);
        }
      }
      c[i][201] = 2;
      G[i].push_back(201);
      G[201].push_back(i);
    }
  }
  if (a != b) {
    cout << "Impossible";
    return 0;
  }
  int flow, fmin;
  for (flow = 0; bfs();) {
    for (auto it : G[201]) {
      if (!viz[it] || f[it][201] == c[it][201]) continue;
      fmin = 1e9;
      t[201] = it;
      for (int nod = 201; nod != 0; nod = t[nod]) {
        fmin = min(fmin, c[t[nod]][nod] - f[t[nod]][nod]);
      }
      if (fmin == 0) continue;
      for (int nod = 201; nod != 0; nod = t[nod]) {
        f[t[nod]][nod] += fmin;
        f[nod][t[nod]] -= fmin;
      }
      flow += fmin;
    }
  }
  if (flow != 2 * a) {
    cout << "Impossible";
    return 0;
  }
  memset(viz, 0, sizeof viz);
  for (int i = 1; i <= n; ++i) {
    if (viz[i] == false) {
      ++cnt;
      Find(i);
    }
  }
  cout << cnt << "\n";
  for (int i = 1; i <= cnt; ++i) {
    cout << ans[i].size() << " ";
    for (auto it : ans[i]) {
      cout << it << " ";
    }
    cout << "\n";
  }
  return 0;
}
