int main() {
#ifdef DEBUG
time_t startt = clock();
#endif
isprime.set();
isprime[0] = isprime[1] = 0;
for(int i = 0; i<20015; i++)
if(isprime[i]) {
for(int j = i*i; j<20015; j+= i)
isprime[j] = 0;
}
scanf("%d", &n);
p.assign(n+2, 0);
q.assign(n+2, 0);
int cnt[] = {0, 0};
s = n; t = n+1;
memset(res, 0, sizeof res);
for(int i = 0; i<n; i++) {
scanf("%d", a+i);
if(a[i] & 1) {
cnt[0]++;
res[s][i] = 2;
}
else {
res[i][t] = 2;
cnt[1]++;
}
}
if(cnt[0] != cnt[1]) {
puts("Impossible");
return 0;
}
for(int i = 1; i<n; i++)
for(int j = 0; j<i; j++)
if(isprime[a[i]+a[j]]) {
if(a[i] & 1)
res[i][j] = 1;
else
res[j][i] = 1;
}
int flow = 0;
n += 2;
while(1) {
f = 0;
vis.reset();
queue< int > q;
p.assign(n, -1);
q.push(s);
vis[s] = 1;
while(!q.empty()) {
int u = q.front(); q.pop();
if(u == t) break;
for(int i = 0; i<n; i++)
if(!vis[i] && res[u][i] > 0)
p[i] = u, vis[i] = 1, q.push(i);
}
augment(t, 1000000);
if(f == 0) break;
flow += f;
}
if(flow != (cnt[0]<<1)) {
puts("Impossible");
return 0;
}
vis.set();
n -= 2;
for(int i = 0; i<n; i++) if(vis[i] && (a[i] & 1)) {
int v = i;
ans.push_back(vi());
while(vis[v]) {
ans.back().push_back(v);
vis[v] = 0;
for(int j = 0; j<n; j++) {
if(vis[j] && ((a[j] & 1) == 0) && res[j][v]) {
v = j;
break;
}
}
ans.back().push_back(v);
vis[v] = 0;
for(int j = 0; j<n; j++)
if(vis[j] && (a[j] & 1) && res[v][j]) {
v = j;
break;
}
}
}
printf("%d\n", ans.size());
for(int i = 0; i<ans.size(); i++) {
printf("%d", ans[i].size());
for(int j = 0; j< ans[i].size(); j++)
printf(" %d", ans[i][j] + 1);
printf("\n");
}
#ifdef DEBUG
cerr << "Running time : " << (double)(clock()-startt) * 1000 / CLOCKS_PER_SEC << " ms" << endl;
int T = time(NULL)-1491365861;
cerr << "Time : " << T/60 << " minutes " << T%60 << " secs" << endl;
#endif
return 0;
}
