You're wrong. n lg n grows asymptotically slower than n^2, and is thus is O(n^2). n is also O(n^2), as is 1, or even sin(n). All of this follows directly from the definition [0].

Also the fact that you're plugging numbers in for n indicates to me that you don't actually understand big O notation, which is surprising since the original article is decent.

[0] https://en.wikipedia.org/wiki/Big_O_notation#Formal_definiti...