#include <bits/stdc++.h>
using namespace std;
int n;
int nums[301];
vector<int> Graph[301];
int Flow[301][301];
int Cap[301][301];
int MaxFlow = 0;
int SOURCE, SINK;
vector<int> Tables[301];
int tL = 0;
void AddEdge(int a, int b) {
  Graph[a].push_back(b);
  Graph[b].push_back(a);
  Cap[a][b] = 1;
  Cap[b][a] = 0;
  Flow[a][b] = 0;
  Flow[b][a] = 0;
  return;
}
bool Prime(int a) {
  int i;
  for (i = 2; i * i <= a; i++) {
    if (a % i == 0) return false;
  }
  return true;
}
bool TFO[301];
vector<int> Path;
bool DFS(int ver) {
  if (TFO[ver]) return false;
  TFO[ver] = true;
  Path.push_back(ver);
  if (ver == SINK) return true;
  int i;
  for (i = 0; i < Graph[ver].size(); i++) {
    if (Flow[ver][Graph[ver][i]] < Cap[ver][Graph[ver][i]]) {
      if (DFS(Graph[ver][i])) return true;
    }
  }
  Path.pop_back();
  return false;
}
void SendFlow() {
  int i;
  for (i = 0; i < (int)Path.size() - 1; i++) {
    Flow[Path[i]][Path[i + 1]]++;
    Flow[Path[i + 1]][Path[i]]--;
  }
  MaxFlow++;
  return;
}
void Clear() {
  memset(TFO, false, sizeof(TFO));
  Path.clear();
  return;
}
void GetTable(int ver) {
  if (TFO[ver]) return;
  TFO[ver] = true;
  Tables[tL].push_back(ver);
  int i;
  for (i = 0; i < Graph[ver].size(); i++) {
    if (Flow[ver][Graph[ver][i]] != 0) {
      GetTable(Graph[ver][i]);
    }
  }
  return;
}
int main() {
  int i, j;
  int evens = 0, odds = 0;
  scanf("%d", &n);
  for (i = 1; i <= n; i++) {
    scanf("%d", &nums[i]);
    if (nums[i] % 2 == 0)
      evens++;
    else
      odds++;
  }
  if (evens != odds) {
    printf("Impossible\n");
    return 0;
  }
  for (i = 1; i <= n; i++) {
    for (j = i + 1; j <= n; j++) {
      if (Prime(nums[i] + nums[j])) {
        if (nums[i] % 2 == 0) {
          AddEdge(i, j);
        } else {
          AddEdge(j, i);
        }
      }
    }
  }
  SOURCE = n + 1;
  SINK = n + 2;
  for (i = 1; i <= n; i++) {
    if (nums[i] % 2 == 0) {
      Graph[SOURCE].push_back(i);
      Graph[i].push_back(SOURCE);
      Flow[SOURCE][i] = 0;
      Flow[i][SOURCE] = 0;
      Cap[SOURCE][i] = 2;
      Cap[i][SOURCE] = 0;
    } else {
      Graph[SINK].push_back(i);
      Graph[i].push_back(SINK);
      Flow[SINK][i] = 0;
      Flow[i][SINK] = 0;
      Cap[i][SINK] = 2;
      Cap[SINK][i] = 0;
    }
  }
  Clear();
  while (DFS(SOURCE)) {
    SendFlow();
    Clear();
  }
  if (MaxFlow != n) {
    printf("Impossible\n");
    return 0;
  }
  memset(TFO, false, sizeof(TFO));
  TFO[SINK] = true;
  TFO[SOURCE] = true;
  for (i = 1; i <= n; i++) {
    if (!TFO[i]) {
      tL++;
      GetTable(i);
    }
  }
  printf("%d\n", tL);
  for (i = 1; i <= tL; i++) {
    printf("%d", Tables[i].size());
    for (j = 0; j < Tables[i].size(); j++) {
      printf(" %d", Tables[i][j]);
    }
    printf("\n");
  }
  return 0;
}
