At 1, 2, 3 The algebraic sum of a plus sign or a minus sign is______ (fill in odd or even numbers)

At 1, 2, 3 The algebraic sum of a plus sign or a minus sign is______ (fill in odd or even numbers)

∵ in 1, 2, 3 In 2005, there are odd numbers in odd numbers, and the sum of these 2005 numbers is odd. When a positive or negative sign is arbitrarily added in front of a number, the parity of the formula will not be changed, that is, the algebraic sum of these 2005 numbers is odd

How to use letters to indicate that n is even, that is, a negative sign, and N is odd, that is, a positive sign?
There is a set of monomials: A & # 178;, - a cubic power, 2, - a quartic power, 3, - a quintic power, 4
Write the nth monomial

General term
[（-1）^(n+1) a^(n+1)]/n

At 1, 2, 3 If we add a positive sign and a negative sign before 1992, are their algebraic sums odd or even?

1--1992
There are 996 odd and even numbers
Add and subtract 996 even numbers, and the result is even
Add and subtract 996 odd numbers, and the result is even
Even and even add and subtract, the result is even
So the algebraic sum is even