#include <bits/stdc++.h>
using namespace ::std;
const unsigned long long maxn = 310;
const unsigned long long inf = 1e9 + 500;
const unsigned long long mod = 1e9 + 7;
const unsigned long long maxm = 2e4 + 500;
unsigned long long a[maxn];
unsigned long long id[maxn];
vector<unsigned long long> ger[maxn];
bool npr[maxm];
bool vis[maxn];
unsigned long long match[maxn][2];
bool tt;
bool dfs(unsigned long long a) {
  vis[a] = 1;
  for (auto u : ger[a]) {
    if (match[u][tt] == -1 || (!vis[match[u][tt]] && dfs(match[u][tt]))) {
      match[a][tt] = u;
      match[u][tt] = a;
      return 1;
    }
  }
  return 0;
}
vector<unsigned long long> vec[maxn];
unsigned long long cnr;
void dfss(unsigned long long a) {
  vis[a] = 1;
  vec[cnr].push_back(a + 1);
  unsigned long long v = match[a][0];
  unsigned long long u = match[a][1];
  if (vis[v] == 0) {
    dfss(v);
  }
  if (vis[u] == 0) {
    dfss(u);
  }
}
int main() {
  for (unsigned long long i = 2; i <= maxm; i++) {
    for (unsigned long long j = i * 2; j < maxm; j += i) {
      npr[j] = 1;
    }
  }
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  unsigned long long n;
  cin >> n;
  unsigned long long bala = 0;
  for (unsigned long long i = 0; i < n; i++) {
    cin >> a[i];
    if (a[i] & 1) {
      bala++;
    } else {
      bala--;
    }
  }
  if (bala != 0) {
    cout << "Impossible";
    return 0;
  }
  for (unsigned long long i = 0; i < n; i++) {
    for (unsigned long long j = i + 1; j < n; j++) {
      if (!npr[a[i] + a[j]]) {
        ger[i].push_back(j);
        ger[j].push_back(i);
      }
    }
  }
  tt = 0;
  for (unsigned long long i = 0; i < maxn; i++) {
    match[i][tt] = -1;
  }
  for (unsigned long long i = 0; i < n; i++) {
    if (a[i] & 1) {
      fill(vis, vis + maxn, 0);
      dfs(i);
    }
  }
  for (unsigned long long i = 0; i < n; i++) {
    ger[i].clear();
    if (match[i][tt] == -1) {
      cout << "Impossible";
      return 0;
    }
  }
  for (unsigned long long i = 0; i < n; i++) {
    for (unsigned long long j = i + 1; j < n; j++) {
      if (!npr[a[i] + a[j]] && match[i][0] != j && match[j][0] != i) {
        ger[i].push_back(j);
        ger[j].push_back(i);
      }
    }
  }
  tt = 1;
  for (unsigned long long i = 0; i < maxn; i++) {
    match[i][tt] = -1;
  }
  for (unsigned long long i = 0; i < n; i++) {
    if (a[i] & 1) {
      fill(vis, vis + maxn, 0);
      dfs(i);
    }
  }
  for (unsigned long long i = 0; i < n; i++) {
    ger[i].clear();
    if (match[i][tt] == -1) {
      cout << "Impossible";
      return 0;
    }
  }
  fill(vis, vis + maxn, 0);
  for (unsigned long long i = 0; i < n; i++) {
    if (vis[i] == 0) {
      dfss(i);
      cnr++;
    }
  }
  cout << cnr << endl;
  for (unsigned long long i = 0; i < cnr; i++) {
    cout << vec[i].size() << ' ';
    for (auto a : vec[i]) {
      cout << a << ' ';
    }
    cout << endl;
  }
}
