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
```
def arithmetic_sequence_sum(a, r, n):
    return n * (a + a + ( n - 1) * r) / 2  
def arithmetic_sequence_sum(a, r, n):
    return n * (a + a + ( n - 1) * r) / 2  