#include <bits/stdc++.h>
using namespace std;
const int NMAX = 210, INF = 0x3f3f3f3f, VMAX = 20010;
int N, A[NMAX], Source, Sink, Flow[NMAX][NMAX], Cap[NMAX][NMAX], Father[NMAX],
    Even, Odd;
bool Used[NMAX], Prime[VMAX];
vector<int> G[NMAX], FlowG[NMAX], CurrentTable;
vector<vector<int> > Ans;
bool BFS() {
  queue<int> Q;
  for (int i = 0; i <= N + 1; ++i) Used[i] = Father[i] = 0;
  Used[Source] = 1;
  Q.push(Source);
  while (!Q.empty()) {
    int Node = Q.front();
    Q.pop();
    if (Node == Sink) return 1;
    for (int i = 0; i < G[Node].size(); ++i) {
      int Vec = G[Node][i];
      if (!Used[Vec] && Cap[Node][Vec] > Flow[Node][Vec])
        Used[Vec] = 1, Father[Vec] = Node, Q.push(Vec);
    }
  }
  return Used[Sink];
}
void DFS(int Node, int StartNode) {
  if (Node == StartNode && CurrentTable.size() >= 3) return;
  CurrentTable.push_back(Node);
  Used[Node] = 1;
  for (int i = 0; i < FlowG[Node].size(); ++i)
    if (!Used[FlowG[Node][i]]) DFS(FlowG[Node][i], StartNode);
}
void BuildGraph() {
  Source = 0;
  Sink = N + 1;
  for (int i = 1; i <= N; ++i)
    if (A[i] % 2 == 1) {
      G[Source].push_back(i);
      G[i].push_back(Source);
      Cap[Source][i] = 2;
    } else {
      G[i].push_back(Sink);
      G[Sink].push_back(i);
      Cap[i][Sink] = 2;
    }
  for (int i = 1; i <= N; ++i)
    for (int j = 1; j <= N; ++j)
      if (A[i] % 2 == 1 && A[j] % 2 == 0 && Prime[A[i] + A[j]]) {
        G[i].push_back(j);
        G[j].push_back(i);
        Cap[i][j] = 1;
      }
}
void MaxFlow() {
  int CntFlow = 0;
  while (BFS()) {
    for (int i = 0; i < G[Sink].size(); ++i) {
      int Vec = G[Sink][i];
      if (Used[Vec] && Cap[Vec][Sink] != Flow[Vec][Sink]) {
        int MinFlow = INF;
        Father[Sink] = Vec;
        for (int Node = Sink; Node != Source; Node = Father[Node])
          MinFlow =
              min(MinFlow, Cap[Father[Node]][Node] - Flow[Father[Node]][Node]);
        for (int Node = Sink; Node != Source; Node = Father[Node]) {
          Flow[Father[Node]][Node] += MinFlow;
          Flow[Node][Father[Node]] -= MinFlow;
        }
        CntFlow += MinFlow;
      }
    }
  }
  if (CntFlow != N)
    printf("Impossible\n");
  else {
    for (int i = 1; i <= N; ++i)
      for (int j = 1; j <= N; ++j)
        if (A[i] % 2 == 1 && A[j] % 2 == 0 && Prime[A[i] + A[j]] &&
            Flow[i][j] == 1)
          FlowG[i].push_back(j), FlowG[j].push_back(i);
    for (int i = 1; i <= N; ++i) Used[i] = 0;
    for (int i = 1; i <= N; ++i)
      if (!Used[i]) {
        CurrentTable.clear();
        DFS(i, i);
        Ans.push_back(CurrentTable);
      }
    printf("%i\n", Ans.size());
    for (int i = 0; i < Ans.size(); ++i) {
      printf("%i ", Ans[i].size());
      for (int j = 0; j < Ans[i].size(); ++j) printf("%i ", Ans[i][j]);
      printf("\n");
    }
    return;
  }
}
int main() {
  for (int i = 2; i < VMAX; ++i) Prime[i] = 1;
  for (int i = 2; i < VMAX; ++i)
    if (Prime[i])
      for (int j = i + i; j < VMAX; j += i) Prime[j] = 0;
  scanf("%i", &N);
  for (int i = 1; i <= N; ++i) {
    scanf("%i", &A[i]);
    Even += (A[i] % 2 == 0);
    Odd += (A[i] % 2 == 1);
  }
  if (Even != Odd) {
    printf("Impossible\n");
    return 0;
  }
  BuildGraph();
  MaxFlow();
  return 0;
}
