In your class, you have started lessons about [arithmetic progression](https://en.wikipedia.org/wiki/Arithmetic_progression). Since you are also a programmer, you have decided to write a function that will return the first `n` elements of the sequence with the given common difference `d` and first element `a`. Note that the difference may be zero!

The result should be a string of numbers, separated by comma and space.

## Example

```python
# first element: 1, difference: 2, how many: 5
arithmetic_sequence_elements(1, 2, 5) == "1, 3, 5, 7, 9"
```

~~~if:fortran
*NOTE: In Fortran, your returned string is* **not** *permitted to contain redundant leading/trailing whitespace.*
~~~

Difficulty: introductory

Starter code:

def arithmetic_sequence_elements(a, r, n):
	

Solutions:
def arithmetic_sequence_elements(a, r, n):
    return ', '.join(str(a + b * r) for b in range(n))


def arithmetic_sequence_elements(a, r, n):
    return ", ".join((str(a+r*i) for i in range(n)))

from itertools import count, islice

def arithmetic_sequence_elements(a, r, n):
    return ', '.join([str(x) for x in islice(count(a, r), n)])

def arithmetic_sequence_elements(a, r, n):
    return ', '.join(str(a + r*x) for x in range(n))

def arithmetic_sequence_elements(a, r, n):
    rng = list(range(a, a + (r * n), r)) if r != 0 else [a] * n
    return ', '.join(map(str,rng))

def arithmetic_sequence_elements(a, r, n):
    z = str(a)
    for i in range(n - 1):
        a = a + r
        z = z + ", " + str(a)

    return z

def arithmetic_sequence_elements(a, r, n):
    def seq(a,r,n):
        while n>0:
            yield a
            n-=1
            a+=r
    return ", ".join(map(str,seq(a,r,n)))


def arithmetic_sequence_elements(a, r, n):
    out = [str(a)]
    for i in range(n - 1):
        a += r
        out.append(str(a))
    
    return ", ".join(out)


def arithmetic_sequence_elements(a, r, n):
    result = str(a)
    list_ = [a]
    for i in range(n-1):
        result += ', ' + str(list_[-1]+r)
        list_.append(list_[-1]+r)
    return result

def arithmetic_sequence_elements(a, r, n):
    result = [str(a)]
    for i in range(1, n):
        a = a + r
        result.append(str(a))
    return ", ".join(result)