Definition of Even and Odd:
* Even = {2k; ForAll k in Z}
* Odd = {2k+1; ForAll k in Z}
Definition of Z:
* The integers are formed by the natural numbers including 0 (0, 1, 2, 3, ...) together with the negatives of the non-zero natural numbers (−1, −2, −3, ...).
0 is Even because:
* 2k[k := 0] is equal to 0.
0 is not Odd because:
* 2k+1[k := (-∞,0):Z] is always negative, and thus not 0.
* 2k+1[k := [0,∞

:Z] is always positive, and thus not 0.
'0' is a number. '0' is not nothing, '0' is an element of Z (Integers), Q (Rational Numbers), R (Reals), C (Complex Numbers) and many more sets. 'Ø' is nothing, the empty set or null set.
Everyone saying that zero isn't a number or isn't even isn't talking about '0', they're talking about 'Ø'. 'Ø' is sometimes, mistakenly, referred to as "zero" in natural language because of the inherent flaws of natural language when it comes to logic (hence the use of formal language).
'Ø' is equal to 0 just as much as the set {A} is equal to 1. 0 is the element count of 'Ø', just like 1 is the element count of {A}.