#include <bits/stdc++.h>
using namespace std;
int n, k;
int l[250];
int r[250];
int rid[250];
int lid[250];
int pr[100500];
int lc, rc;
int cnt1, cnt2;
int nn[250];
int py[250];
int py2[250];
int px2[250];
vector<int> g[250];
vector<int> ans[250];
int c;
bool rec(int v) {
  if (nn[v]) return false;
  nn[v] = true;
  for (int i = 0; i < g[v].size(); ++i) {
    int x = g[v][i];
    if (py[x] == -1 || rec(py[x])) {
      py[x] = v;
      return true;
    }
  }
  return false;
}
bool rec2(int v) {
  if (nn[v]) return false;
  nn[v] = true;
  for (int i = 0; i < g[v].size(); ++i) {
    int x = g[v][i];
    if (x == -1) continue;
    if (py2[x] == -1 || rec2(py2[x])) {
      py2[x] = v;
      return true;
    }
  }
  return false;
}
void go(int v, int c) {
  if (nn[v]) return;
  nn[v] = true;
  ans[c].push_back(rid[v]);
  v = py[v];
  ans[c].push_back(lid[v]);
  v = px2[v];
  go(v, c);
}
int main() {
  for (int i = 2; i < 100500; ++i) pr[i] = true;
  for (int i = 2; i < 100500; ++i) {
    for (int j = i + i; j < 100500; j += i) pr[j] = false;
  }
  scanf("%i", &n);
  for (int i = 0; i < n; ++i) {
    int x;
    scanf("%i", &x);
    if (x % 2 == 0) {
      l[lc] = x;
      lid[lc] = i;
      lc++;
    } else {
      r[rc] = x;
      rid[rc] = i;
      rc++;
    }
  }
  if (lc != rc) {
    printf("Impossible\n");
    return 0;
  }
  k = lc;
  for (int i = 0; i < k; ++i)
    for (int j = 0; j < k; ++j)
      if (pr[l[i] + r[j]]) g[i].push_back(j);
  for (int i = 0; i < k; ++i) py[i] = -1;
  for (int i = 0; i < k; ++i) {
    memset(nn, 0, sizeof(nn));
    if (rec(i)) cnt1++;
  }
  if (cnt1 != k) {
    printf("Impossible\n");
    return 0;
  }
  for (int i = 0; i < k; ++i) {
    int x = py[i];
    for (int j = 0; j < g[x].size(); ++j)
      if (g[x][j] == i) g[x][j] = -1;
  }
  for (int i = 0; i < k; ++i) py2[i] = -1;
  for (int i = 0; i < k; ++i) {
    memset(nn, 0, sizeof(nn));
    if (rec2(i)) cnt2++;
  }
  if (cnt2 != k) {
    printf("Impossible\n");
    return 0;
  }
  for (int i = 0; i < k; ++i) {
    px2[py2[i]] = i;
  }
  memset(nn, 0, sizeof(nn));
  for (int i = 0; i < k; ++i)
    if (!nn[i]) {
      go(i, c);
      c++;
    }
  printf("%i\n", c);
  for (int i = 0; i < c; ++i) {
    printf("%i", ans[i].size());
    for (int j = 0; j < ans[i].size(); ++j) printf(" %i", ans[i][j] + 1);
    printf("\n");
  }
  return 0;
}
