Off-by-one in Sigma

[Dalton-Gray]

sum([k for k in range(100)])

output: 4950

The reference said output: 5050
Which would be

sum([i for i in range(101)])

[tobiaszwingmann]

The second example of sigma is also wrong. The result should be 10200. Better define a custom function instead of using range like so:

def my_range(i):
  return([k+1 for k in range(i)])

and then call

sum([2*k + 1 for k in my_range(100)])