Student: Find the odd man out\n1, 3, 7, 11, 15, 18, 21\nOptions:\n(A) 3\n(B) 7\n(C) 18\n(D) 21\n(E) 1.
Another student: Let's say, hmmm...

User
The 18 is the only even number in the series. Final answer: (C).
Assistant