def triangle_number(n):
    """Get the nth triangle number

    1: 1 = 1
    2: 1 + 2 = 3
    3: 1 + 2 + 3 = 6
    4: 1 + 2 + 3 + 4 = 10

    Test cases:
    - 012
    """
    triangle = (n * (n + 1)) / 2
    return triangle