[0, 2, 6, 12, 20, 30, 42, 56, 72, 90]

g = lambda x: x + g(x - 2) if x > 0 else 0
print([g(2 * i) for i in range(10)])

>>> [x*(x + 1) for x in range(10)]
[0, 2, 6, 12, 20, 30, 42, 56, 72, 90]