Arithmetic sequence - sum of n elements.js

/*
Description:
In your class, you have started lessons about "arithmetic progression". Because you are also a programmer, you have decided to write a function.

This function, arithmetic_sequence_sum(a, r, n), should return the sum of the first (n) elements of a sequence in which each element is the sum of the given integer (a), and a number of occurences of the given integer (r), based on the element's position within the sequence.

For example:

arithmetic_sequence_sum(2, 3, 5) should return 40:

1     2        3          4            5
a + (a+r) + (a+r+r) + (a+r+r+r) + (a+r+r+r+r) 
2 + (2+3) + (2+3+3) + (2+3+3+3) + (2+3+3+3+3) = 40
*/

function ArithmeticSequenceSum(a, r, n) {
 let arr=[];
 for (let i=0;i<n;i++)
 arr.push(a+r*i)
  return arr.reduce((a,b)=>a+b,0)
}