#include <bits/stdc++.h>
using namespace std;
int p[40010] = {0};
int adj[1001][1001];
int parent[2100];
vector<int> v[501];
int sz = 0;
int vis[501], a[501];
int bfs(int graph[][1001], int v, int t, int s) {
  int visited[1001] = {0}, i, u;
  queue<int> q;
  q.push(s);
  visited[s] = 1;
  for (i = 0; i <= v; i++) parent[i] = -1;
  while (!q.empty()) {
    u = q.front();
    q.pop();
    for (i = 0; i < v; i++) {
      if (graph[u][i] > 0 && visited[i] == 0) {
        q.push(i);
        parent[i] = u;
        visited[i] = 1;
      }
    }
  }
  return visited[t];
}
int maxflow(int graph[][1001], int s, int t, int V) {
  int maxflow = 0, pathflow, v;
  while (bfs(graph, V, t, s)) {
    pathflow = 1000000000;
    for (v = t; v != s; v = parent[v])
      pathflow = min(pathflow, graph[parent[v]][v]);
    maxflow += pathflow;
    for (v = t; v != s; v = parent[v]) {
      graph[v][parent[v]] += pathflow;
      graph[parent[v]][v] -= pathflow;
    }
  }
  return maxflow;
}
void dfs(int u, int n) {
  if (u > n) {
    for (int i = 1; i <= n; i++)
      if (adj[u][i] > 0 && !vis[i]) {
        vis[i] = 1;
        v[sz].push_back(i);
        dfs(i, n);
      }
  } else {
    for (int i = n + 1; i <= 2 * n; i++)
      if (adj[i][u] > 0 && !vis[i]) {
        vis[i] = 1;
        v[sz].push_back(i - n);
        dfs(i, n);
      }
  }
}
int main() {
  int n, i, j, e = 0, o = 0;
  for (i = 2; i <= 200; i++)
    if (p[i] == 0)
      for (j = i + i; j <= 40000; j += i) p[j] = 1;
  cin >> n;
  for (i = 0; i < n; i++) {
    cin >> a[i];
    if (a[i] % 2 == 0)
      e++;
    else
      o++;
  }
  if (e != o) {
    printf("Impossible\n");
    return 0;
  }
  for (i = 0; i <= 2 * n + 1; i++)
    for (j = 0; j <= 2 * n + 1; j++) adj[i][j] = 0;
  for (i = 0; i < n; i++)
    for (j = i + 1; j < n; j++)
      if (p[a[i] + a[j]] == 0) {
        if (a[i] % 2 == 1)
          adj[i + 1][j + n + 1] = 1;
        else
          adj[j + 1][i + n + 1] = 1;
      }
  for (i = 1; i <= n; i++)
    if (a[i - 1] % 2 == 1) adj[0][i] = 2;
  for (i = 1; i <= n; i++)
    if (a[i - 1] % 2 == 0) adj[i + n][2 * n + 1] = 2;
  int ans = maxflow(adj, 0, 2 * n + 1, 2 * n + 2);
  if (ans != n) {
    printf("Impossible\n");
    return 0;
  }
  sz = 0;
  for (i = n + 1; i <= 2 * n; i++) {
    if (!vis[i] && a[i - n - 1] % 2 == 0) {
      vis[i] = 1;
      v[sz].push_back(i - n);
      dfs(i, n);
      sz++;
    }
  }
  assert(sz <= n / 3);
  printf("%d\n", sz);
  for (i = 0; i < sz; i++) {
    printf("%d ", v[i].size());
    for (j = 0; j < v[i].size(); j++) printf("%d ", v[i][j]);
    printf("\n");
  }
  return 0;
}
