#include <bits/stdc++.h>
using namespace std;
int i, j, n, e = 0, o = 0, k;
int age[202], FLOW = 0;
int cap[202][202];
int flow[202][202];
int visit[202], por[202];
int prime[20002];
int tc = 0;
queue<int> q, t[202];
void genprime(int m) {
  prime[1] = -1;
  for (i = 2; i <= m; i++) {
    if (prime[i] == 0) {
      prime[i] = 1;
      for (j = 2; j * i <= m; j++) {
        prime[j * i] = -1;
      }
    }
  }
  return;
}
void bfs() {
  if (q.front() == n + 1) {
    FLOW++;
    k = n + 1;
    while (k != 0) {
      flow[por[k]][k]++;
      flow[k][por[k]]--;
      k = por[k];
    }
    for (i = 0; i <= n + 1; i++) {
      visit[i] = 0;
    }
    while (!q.empty()) {
      q.pop();
    }
    visit[0] = 1;
    q.push(0);
  } else {
    for (i = 0; i <= n + 1; i++) {
      if (cap[q.front()][i] - flow[q.front()][i] > 0 and visit[i] == 0) {
        por[i] = q.front();
        visit[i] = 1;
        q.push(i);
      }
    }
    q.pop();
  }
  return;
}
void dfs(int p) {
  visit[p] = 1;
  t[tc].push(p);
  for (j = 1; j <= n; j++) {
    if (flow[p][j] != 0 and visit[j] == 0) {
      dfs(j);
      break;
    }
  }
  return;
}
int main() {
  genprime(20000);
  scanf("%d", &n);
  for (i = 1; i <= n; i++) {
    scanf("%d", &age[i]);
    if (age[i] % 2 == 0) {
      cap[0][i] = 2;
      e++;
    } else {
      cap[i][n + 1] = 2;
      o++;
    }
  }
  if (e != o) {
    printf("Impossible");
    return 0;
  }
  for (i = 1; i <= n; i++) {
    for (j = i + 1; j <= n; j++) {
      if (prime[age[i] + age[j]] == 1) {
        if (age[i] % 2 == 0) {
          cap[i][j] = 1;
        } else {
          cap[j][i] = 1;
        }
      }
    }
  }
  visit[0] = 1;
  q.push(0);
  while (!q.empty()) {
    bfs();
  }
  if (FLOW != n) {
    printf("Impossible");
    return 0;
  }
  for (i = 0; i <= n + 1; i++) {
    visit[i] = 0;
  }
  for (i = 1; i <= n; i++) {
    if (visit[i] == 0) {
      tc++;
      dfs(i);
    }
  }
  printf("%d\n", tc);
  for (i = 1; i <= tc; i++) {
    printf("%d ", t[i].size());
    while (!t[i].empty()) {
      printf("%d ", t[i].front());
      t[i].pop();
    }
    printf("\n");
  }
  return 0;
}
