#include <bits/stdc++.h>
namespace G {
int n, m, S, T;
struct Edge {
  int from, to, cap, nxt;
} e[100000 * 2 + 10];
int head[10000 + 10], cur[10000 + 10], cnt;
inline void Init() { memset(head, -1, sizeof(head)), cnt = -1; }
inline void AddEdge(int u, int v, int w) {
  e[++cnt] = (Edge){u, v, w, head[u]}, head[u] = cnt;
  e[++cnt] = (Edge){v, u, 0, head[v]}, head[v] = cnt;
}
int dep[10000 + 10];
bool Dinic_BFS() {
  std::queue<int> q;
  q.push(S);
  memset(dep, 0, sizeof(dep));
  dep[S] = 1;
  while (!q.empty()) {
    int x = q.front();
    q.pop();
    for (int i = head[x]; ~i; i = e[i].nxt)
      if (e[i].cap > 0 && dep[e[i].to] == 0)
        dep[e[i].to] = dep[x] + 1, q.push(e[i].to);
  }
  return dep[T];
}
int Dinic_DFS(int u, int now) {
  if (u == T) return now;
  int ret = 0;
  for (int &i = cur[u]; ~i; i = e[i].nxt)
    if (dep[e[i].to] == dep[u] + 1 && e[i].cap) {
      int di = Dinic_DFS(e[i].to,
                         ((e[i].cap) < (now - ret) ? (e[i].cap) : (now - ret)));
      if (di) {
        e[i].cap -= di, e[i ^ 1].cap += di, ret += di;
        if (ret == now) break;
      }
    }
  return ret;
}
inline int Dinic() {
  int ret = 0;
  while (Dinic_BFS()) {
    memcpy(cur, head, sizeof(head));
    ret += Dinic_DFS(S, (1 << 30));
  }
  return ret;
}
bool vis[10000 + 10];
std::vector<int> cir[10000 + 10];
void DFS(int u, int t) {
  vis[u] = true, cir[t].push_back(u);
  for (int i = head[u]; ~i; i = e[i].nxt)
    if (!vis[e[i].to] && e[i | 1].cap == 1) DFS(e[i].to, t);
}
}  // namespace G
bool Prime(int t) {
  for (int i = 2; i * i <= t; i++)
    if (t % i == 0) return false;
  return true;
}
const int S = 10000 - 2, T = 10000 - 1;
int a[10000 + 10];
int main() {
  G::Init();
  int n;
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
    if (a[i] & 1)
      G::AddEdge(S, i, 2);
    else
      G::AddEdge(i, T, 2);
  }
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= n; j++)
      if (a[i] & 1 && !(a[j] & 1) && Prime(a[i] + a[j])) G::AddEdge(i, j, 1);
  G::S = S, G::T = T, G::n = n;
  if (G::Dinic() != n) {
    puts("Impossible");
    return 0;
  }
  int ans = 0;
  for (int i = 1; i <= n; i++)
    if (!G::vis[i]) G::DFS(i, ++ans);
  printf("%d\n", ans);
  for (int i = 1; i <= ans; i++) {
    printf("%d ", G::cir[i].size());
    for (auto t : G::cir[i]) printf("%d ", t);
    puts("");
  }
  return 0;
}
