diff --git a/Codechef-2021/SEPT21C/Prefix_Sums.cpp b/Codechef-2021/SEPT21C/Prefix_Sums.cpp
new file mode 100644
index 0000000..46f4905
--- /dev/null
+++ b/Codechef-2021/SEPT21C/Prefix_Sums.cpp
@@ -0,0 +1,55 @@
+#pragma GCC optimize ("trapv")
+#include <bits/stdc++.h>
+#include<algorithm>
+#include <vector>
+#include<cstring>
+#include<cstdlib>
+#include<cmath>
+#include<cstdlib>
+#include<sstream>
+#include <string.h>
+using namespace std;
+#define pb push_back
+#define all(v) v.begin(),v.end()
+#define  rep(i,n,v) for(i=n;i<v;i++)
+#define per(i,n,v) for(i=n;i>v;i--)
+#define ff first 
+#define ss second 
+#define pp pair<ll,ll>
+#define ll  long long
+#define ld  long double
+#define endl "\n"
+ 
+const ll mod=1e9+7;
+void solve()
+{
+ll  n, a=0,b=0,m=1, c=-1,k=0, i=0, j=0, l=1e9+5;
+string s,p, q;
+    cin>>n;
+    a=(n*(n+1))/2;
+    if(n%2 || a%2) cout<<"NO"<<endl;
+    else{
+        cout<<"YES"<<endl;
+        vector<ll>v,vec;
+        rep(i,1,n+1){
+            if(i<=(n/4) || i>n-n/4) v.pb(i);
+            else vec.pb(i);
+        }
+        rep(i,0,v.size()) cout<<v[i]<<" ";
+        cout<<endl;
+        rep(i,0,vec.size()) cout<<vec[i]<<" ";
+        cout<<endl;
+    }
+}
+int main()
+{
+ios_base::sync_with_stdio(false);
+cin. tie(0);cout. tie(0);
+ll t=1;
+cin>>t;
+while(t--)
+{
+solve();
+}
+return 0;
+}
\ No newline at end of file