# SEQSUM - Editorial

Author: Rishabh Rathi
Tester: Rishabh Rathi

CAKEWALK

Maths

# PROBLEM:

You are given a sequence - 11, 17, 23, 29, ……

You need to find the total number of sweets needed to distribute among the first N children (sum of first N elements).

# EXPLANATION:

The sequence given is an Arithmetic Progression. Here, first term (a) is 11 and common difference (d) is 6.

Sum of N terms of arithmetic progression, \sum_{i = 1}^{N} a_i

= \frac{N [2a + (n – 1)d]}{2}

=\frac{N [2*11 + (N – 1)*6]}{2}

=\frac{N [22 + 6N - 6]}{2}

=\frac{N [16 + 6N]}{2}

=N [8 + 3N]

# SOLUTIONS:

Setter's Solution (Python)
import sys
def input():

mod = 10**9 + 7

t = int(input())
for _ in range(t):
n = int(input())
ans = (n*(8 + 3*n))%mod
print(ans)

Tester's Solution (CPP)
#include <bits/stdc++.h>
using namespace std;

const int mod = 1e9 + 7;

int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);

long long int n, ans;
int t; cin>>t;

while(t--) {
cin>>n;
ans = ((n%mod) * (8 + 3*n)%mod)%mod;
cout<<ans<<"\n";
}
return 0;
}


Feel free to share your approach. In case of any doubt or anything is unclear, please ask it in the comments section. Any suggestions are welcome