#include <bits/stdc++.h>
using namespace std;
const int MAX = 1e5 + 40;
const int MAXE = 3e5 + 400;
const int MAXN = 800 + 50;
const int INF = 1e9 + 5;
int n, ec, cnt;
int from[2 * MAXE], to[2 * MAXE], cap[2 * MAXE], prv[2 * MAXE];
int head[MAXN], age[MAXN];
bool mark[MAXN];
vector<int> od, ev, ans[MAXN], sec[MAXN], adj[MAXN];
bool pr[MAX];
int fs[2 * MAXE];
void init() {
  pr[0] = pr[1] = 1;
  for (int i = 2; i < MAX; i++)
    for (int j = i + i; j < MAX; j += i) pr[j] = 1;
  memset(head, -1, sizeof(mark));
}
void add_edge(int u, int v, int uv, int vu = 0) {
  fs[ec] = uv;
  from[ec] = u, to[ec] = v, cap[ec] = uv, prv[ec] = head[u];
  head[u] = ec++;
  fs[ec] = vu;
  from[ec] = v, to[ec] = u, cap[ec] = vu, prv[ec] = head[v], head[v] = ec++;
}
int dfs(int v, int sink, int mini = INF) {
  if (v == sink) return mini;
  if (mark[v]) return 0;
  mark[v] = 1;
  for (int e = head[v]; e != -1; e = prv[e])
    if (cap[e]) {
      int x = dfs(to[e], sink, min(mini, cap[e]));
      if (x == 0) continue;
      cap[e] -= x;
      cap[e ^ 1] += x;
      return x;
    }
  return 0;
}
int max_flow(int root, int sink) {
  memset(mark, 0, sizeof(mark));
  int ret = 0, x;
  while ((x = dfs(root, sink))) {
    ret += x;
    memset(mark, 0, sizeof(mark));
  }
  return ret;
}
void get(int v) {
  if (mark[v]) return;
  mark[v] = 1;
  ans[cnt].push_back(v);
  for (int u : sec[v]) get(u);
}
int main() {
  init();
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> age[i];
    if (age[i] % 2 == 0)
      ev.push_back(i);
    else
      od.push_back(i);
  }
  for (int i = 0; i < ev.size(); i++)
    for (int j = 0; j < od.size(); j++)
      if (!pr[age[ev[i]] + age[od[j]]]) add_edge(ev[i], od[j], 1);
  int temp = ec;
  for (int u : ev) add_edge(n, u, 2);
  for (int u : od) add_edge(u, n + 1, 2);
  if (od.size() != ev.size() || max_flow(n, n + 1) != 2 * (int)ev.size())
    cout << "Impossible\n";
  else {
    for (int i = 0; i < temp; i += 2)
      if (fs[i] != cap[i]) {
        sec[from[i]].push_back(to[i]);
        sec[to[i]].push_back(from[i]);
      }
    memset(mark, 0, sizeof(mark));
    for (int i = 0; i < n; i++)
      if (!mark[i]) get(i), cnt++;
    cout << cnt << endl;
    for (int i = 0; i < cnt; i++) {
      cout << ans[i].size() << " ";
      for (int u : ans[i]) cout << u + 1 << " ";
      cout << endl;
    }
  }
  return 0;
}
