#include <bits/stdc++.h>
using namespace std;
struct bian {
  int next, point, f;
} b[80000];
int a[300], n, totpoin, dst[300], pd[300], p[300], len, B[300][300], tot,
    x[300], totpoint, inf = 1e5;
vector<int> A[300];
void dfs(int k) {
  A[tot].push_back(k);
  pd[k] = 1;
  for (int i = 1; i <= n; i++)
    if (B[k][i] && pd[i] == 0) dfs(i);
}
void ade(int k1, int k2, int k3) {
  len++;
  b[len].point = k2;
  b[len].next = p[k1];
  b[len].f = k3;
  p[k1] = len;
}
void add(int k1, int k2, int k3) {
  ade(k1, k2, k3);
  ade(k2, k1, 0);
}
bool bfs() {
  int head = 1, now = 0, i, j;
  memset(dst, 0xff, sizeof dst);
  memset(pd, 0x00, sizeof pd);
  x[1] = 0;
  pd[0] = 1;
  dst[0] = 0;
  while (head > now) {
    now++;
    i = p[x[now]];
    while (i != -1) {
      j = b[i].point;
      if ((b[i].f) && (!pd[j])) {
        pd[j] = 1;
        dst[j] = dst[x[now]] + 1;
        if (j == totpoint) {
          return 1;
        }
        head++;
        x[head] = j;
      }
      i = b[i].next;
    }
  }
  return pd[totpoint];
}
int change(int k1, int k2) {
  if ((k1 == totpoint) || (k2 == 0)) return k2;
  int num = 0, k, i, j;
  i = p[k1];
  while (i != -1) {
    j = b[i].point;
    if ((b[i].f) && (dst[k1] + 1 == dst[j])) {
      k = change(j, min(k2, b[i].f));
      k2 = k2 - k;
      num += k;
      b[i].f = b[i].f - k;
      b[i ^ 1].f += k;
      if (k2 == 0) {
        break;
      }
    }
    i = b[i].next;
  }
  if (!num) {
    dst[k1] = -1;
  }
  return num;
}
int dinic() {
  int now = 0;
  while (bfs()) now += change(0, inf);
  return now;
}
int check(int k) {
  for (int i = 2; i * i <= k; i++)
    if (k % i == 0) return 0;
  return 1;
}
int main() {
  scanf("%d", &n);
  memset(p, 0xff, sizeof p);
  len = -1;
  for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
  for (int i = 1; i <= n; i++)
    if (a[i] % 2)
      add(0, i, 2);
    else
      add(i, n + 1, 2);
  for (int i = 1; i <= n; i++)
    if (a[i] % 2)
      for (int j = 1; j <= n; j++)
        if ((a[j] % 2 == 0) && (check(a[i] + a[j]))) {
          add(i, j, 1);
        }
  totpoint = n + 1;
  if (dinic() != n) {
    printf("Impossible\n");
    return 0;
  }
  for (int i = 1; i <= n; i++)
    if (a[i] % 2)
      for (int j = p[i]; j != -1; j = b[j].next)
        if (j % 2 == 0 && b[j].f == 0) {
          B[i][b[j].point] = 1;
          B[b[j].point][i] = 1;
        }
  memset(pd, 0x00, sizeof pd);
  for (int i = 1; i <= n; i++)
    if (pd[i] == 0) {
      tot++;
      dfs(i);
    }
  cout << tot << endl;
  for (int i = 1; i <= tot; i++) {
    cout << A[i].size() << " ";
    for (int j = 0; j < A[i].size(); j++) cout << A[i][j] << " ";
    cout << endl;
  }
  return 0;
}
