Your task is to return the sum of Triangular Numbers up-to-and-including the `nth` Triangular Number.
Triangular Number: "any of the series of numbers (1, 3, 6, 10, 15, etc.) obtained by continued summation of the natural numbers 1, 2, 3, 4, 5, etc."
```
[01]
02 [03]
04 05 [06]
07 08 09 [10]
11 12 13 14 [15]
16 17 18 19 20 [21]
```
e.g. If `4` is given: `1 + 3 + 6 + 10 = 20`.
Triangular Numbers cannot be negative so return 0 if a negative number is given.
def sum_triangular_numbers(n):
    return 0 if n <= 0 else sum([i for i in range(1, n+1)]) + sum_triangular_numbers(n-1)
def sum_triangular_numbers(n):
    return 0 if n <= 0 else sum([i for i in range(1, n+1)]) + sum_triangular_numbers(n-1)