The sum of the even numbers between 1 and n is 81*82, where n is an odd number, then n=?	Choose the correct choice.
A) 163 B) 171 C) 177 D) 185 E) 193

Rationale: "let n - 1 = 2 a . 2 + 4 + . . . + 2 a = 2 * ( 1 + 2 + . . . + a ) = 2 * ( a ) ( a + 1 ) / 2 = ( a ) ( a + 1 ) = 81 * 82 then a = 81 and n = 163 . the answer is a ."
Answer: A