void sol(){
if(s2<s1){
vi t=a;a=b;b=t;
ll x=s1;s1=s2;s2=x;
t=ida;ida=idb;idb=t;
fliped=!fliped;
}
if(a.empty() || b.empty())return ;
if(abs(s1-s2)==0){return ;}
ll diff = abs(s2 - s1);
ll Y = diff;
int x,y;
x=y=0;
// printf("diff = %lld\n",diff);
for (int i = 0; i < a.size(); ++i) {
vi::iterator it = lower_bound(b.begin(), b.end(), diff/2 + a[i]);
int j = it-b.begin();
if(j && j == b.size())j--;
// printf("i,j=%d,%d\n",i,j);
ll ns1 = s1 - a[i] + b[j];
ll ns2 = s2 - b[j] + a[i];
// printf("debug a[%d] = %d b[%d] = %d\n",i,a[i],j,b[j]);
// printf("debug ns1 = %lld ns2 = %lld\n",ns1,ns2);
if(abs(ns1 - ns2) < Y){
x = i;
y = j;
// printf("debug %d %d\n",x,y);
Y = abs(ns1 - ns2);
}
}
if(Y<diff){
// printf("swaping a[%d] b[%d] diff = %lld\n", x,y, Y);
if(fliped)
ans.push_back(ii(idb[y],ida[x]));
else
ans.push_back(ii(ida[x],idb[y]));
s1 = s1 - a[x] + b[y];
s2 = s2 + a[x] - b[y];
}
// printf("x,y = %d %d\n",x,y);
a.erase(move(a,x));
ida.erase(move(ida,x));
b.erase(move(b,y));
idb.erase(move(idb,y));
}
bool query(const vvpi& T, const vi& Qin)
{
if ( Qin.empty() ) return true;
if ( Qin.size() == 1 ) return !T[ Qin[0] ].empty();
auto Q = Qin; // copy the query
sort(Q.begin(), Q.end());
for ( auto p : T[ Q[0] ] )
{
int i, k; tie(i, k) = p;
int s = 1;
while ( k <= Q[s] && k > -1 )
{
s += k == Q[s];
if ( s == Q.size() )
return true;
auto it = lower_bound( T[k].begin(), T[k].end(), i,
[](const pi& x, int val) -> bool { return x.first < val; } );
if (it == T[k].end() || it->first != i)
break;
k = it->second;
}
}
return false;
}
bool query(const vvi& T, const vi& Q)
{
if ( Q.empty() ) return true;
vi S = T[ Q[0] ];
if ( Q.size() == 1 ) return !S.empty();
for ( int i = 1; i < Q.size(); ++i )
{
const auto& TQi = T[ Q[i] ];
workspace_vec.clear();
set_intersection( S.begin(), S.end(), TQi.begin(), TQi.end(),
back_inserter(workspace_vec));
S = workspace_vec;
if ( S.empty() )
return false;
}
return !S.empty();
}
void out(vi & a)
{
printf("%d", a.empty() ? 0 : a.back());
for (int i = int(a.size()) - 2; i >= 0; i--)
printf("%09d", a[i]);
}
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;
}