#include <bits/stdc++.h>
using namespace std;
const int N = 205, INF = 1e9;
int n, st, en, cnt;
int a[N], c[N][N], f[N][N], pa[N];
vector<int> adj[N], ans[N];
bool used[N];
bool check(int x) {
  int sqr = sqrt(x);
  for (int i = 2; i <= sqr; ++i)
    if (x % i == 0) return false;
  return true;
}
bool bfs() {
  memset(pa, -1, sizeof pa);
  pa[st] = INF;
  queue<int> q;
  q.push(st);
  while (!q.empty()) {
    int u = q.front();
    q.pop();
    for (int i = 0; i <= (int)adj[u].size() - 1; ++i) {
      int v = adj[u][i];
      if (pa[v] == -1 && c[u][v] > f[u][v]) {
        pa[v] = u;
        q.push(v);
      }
    }
  }
  return (pa[en] != -1);
}
void solve() {
  int v = en, u, res = INF;
  while (v != st) {
    u = pa[v];
    res = min(res, c[u][v] - f[u][v]);
    v = u;
  }
  v = en;
  while (v != st) {
    u = pa[v];
    f[u][v] += res;
    f[v][u] -= res;
    v = u;
  }
}
void find(int u) {
  used[u] = true;
  ans[cnt].push_back(u);
  for (int i = 0; i <= (int)adj[u].size() - 1; ++i) {
    int v = adj[u][i];
    if (v != st && v != en && not used[v] && abs(f[u][v]) == 1) {
      find(v);
      return;
    }
  }
}
signed main() {
  cin >> n;
  st = 0;
  en = n + 1;
  for (int i = 1; i <= n; ++i) cin >> a[i];
  for (int i = 1; i <= n; ++i) {
    if (a[i] & 1) {
      adj[st].push_back(i);
      adj[i].push_back(st);
      c[st][i] = 2;
    } else {
      adj[i].push_back(en);
      adj[en].push_back(i);
      c[i][en] = 2;
    }
    for (int j = 1; j <= n; ++j)
      if (check(a[i] + a[j]) && a[i] & 1) {
        adj[i].push_back(j);
        adj[j].push_back(i);
        c[i][j] = 1;
      }
  }
  while (bfs()) solve();
  for (int i = 0; i <= (int)adj[st].size() - 1; ++i) {
    int u = adj[st][i];
    if (f[st][u] != 2) {
      cout << "Impossible";
      return 0;
    }
  }
  for (int i = 0; i <= (int)adj[en].size() - 1; ++i) {
    int u = adj[en][i];
    if (f[u][en] != 2) {
      cout << "Impossible";
      return 0;
    }
  }
  used[st] = used[en] = true;
  for (int i = 1; i <= n; ++i) {
    if (not used[i]) {
      find(i);
      cnt++;
    }
  }
  cout << cnt << "\n";
  for (int i = 0; i <= cnt - 1; ++i) {
    cout << ans[i].size() << " ";
    for (int j = 0; j <= (int)ans[i].size() - 1; ++j) cout << ans[i][j] << ' ';
    cout << "\n";
  }
}
