#include <bits/stdc++.h>
using namespace std;
int N;
int A[205];
int cnt[2];
bitset<20005> compo;
int cap[205][205];
int par[205];
int macflow;
vector<int> pp[205];
vector<int> adj[205];
void edge(int u, int v, int c) {
  cap[u][v] = c;
  adj[u].push_back(v);
  adj[v].push_back(u);
}
void match(int u, int v) {
  pp[u].push_back(v);
  pp[v].push_back(u);
}
void input() {
  scanf("%d", &N);
  for (int i = 2; i <= 20000; i++) {
    if (compo[i]) continue;
    for (int j = i * i; j <= 20000; j += i) {
      compo[j] = 1;
    }
  }
  for (int i = 1; i <= N; i++) {
    scanf("%d", &A[i]);
    if (A[i] & 1)
      edge(0, i, 2);
    else
      edge(i, 201, 2);
    for (int j = 1; j < i; j++) {
      if (compo[A[i] + A[j]] == 0) {
        if (A[i] & 1)
          edge(i, j, 1);
        else
          edge(j, i, 1);
      }
    }
  }
}
void DFS(int u) {
  if (u == 201) return;
  for (int v : adj[u]) {
    if (cap[u][v] == 0) continue;
    if (par[v] == -1) {
      par[v] = u;
      DFS(v);
    }
    if (par[201] != -1) return;
  }
}
int augment(int u, int c) {
  if (u == 0) return c;
  if (par[u] != -1) {
    int flow = augment(par[u], min(c, cap[par[u]][u]));
    cap[par[u]][u] -= flow;
    cap[u][par[u]] += flow;
    return flow;
  }
  return 0;
}
bool vis[205];
int pa;
vector<int> res[100];
void DFS2(int u, int p) {
  vis[u] = 1;
  res[pa].push_back(u);
  for (int v : pp[u]) {
    if (vis[v]) continue;
    DFS2(v, u);
  }
}
void ford() {
  while (1) {
    memset(par, -1, sizeof(par));
    par[0] = -2;
    DFS(0);
    int flow = augment(201, 1000000);
    if (flow == 0) break;
    macflow += flow;
  }
  if (macflow != N) {
    puts("Impossible");
    return;
  }
  for (int i = 1; i <= N; i++) {
    for (int j = i + 1; j <= N; j++) {
      if (compo[A[i] + A[j]] == 0) {
        if (A[i] & 1) {
          if (cap[j][i] == 1) {
            match(i, j);
          }
        } else {
          if (cap[i][j] == 1) {
            match(i, j);
          }
        }
      }
    }
  }
  for (int i = 1; i <= N; i++) {
    if (vis[i]) continue;
    pa++;
    DFS2(i, 0);
  }
  printf("%d\n", pa);
  for (int i = 1; i <= pa; i++) {
    printf("%d ", (int)res[i].size());
    for (int now : res[i]) {
      printf("%d ", now);
    }
    putchar('\n');
  }
  cin >> N;
}
int main() {
  input();
  ford();
}
