# Problem Link:

*Author:* Nikhil Raghav

*Tester:* Nikhil Raghav

*Editorialist:* Nikhil Raghav

# Difficulty

Cakewalk

# Problem

Given a pattern, observe it and find the sum of first N terms of the series.

# Explanation

You were given a pattern, which goes like this: 1, 6, 12, 18, 24 …

This is moreover an AP when it starts from the second element.

You just need to find out the sum of AP.

We can write the series as : 1 + 6*(1 + 2 + 3 + .... + Z) … (Equation 1)

Z will be (total number of concentric hexagons - 1) which is N/6.

Sum of the first Z elements can be written as : (Z * (Z + 1) )/2 … (Equation 2)

Now, just replace the value from Equation 2 in Equation 1,

1 + 6*( ( Z * ( Z + 1 ) ) / 2)

where Z = N/6

# Solution

## Author's Solution

#include<bits/stdc++.h>

using namespace std;

int main()

{

int t;

cin>>t;

long long n;

while(t–)

{

scanf("%lld",&n);

if(n==1){printf(“1\n”);continue;}

long long z = n/6, ans=1+ 6*((z*(z+1))/2);

printf("%lld\n",ans);

}

}