Which operations is the following set closed under: {... , -3, -1, 1, 3, ...}?

Question

Which operations is the following set closed under: {... , -3, -1, 1, 3, ...}?

Answer 1

{...-5,-3,-1,1,3,5,...}

this set is not closed under addition

example:1+3=4 which is not in the set

this set is not closed under subtraction

example: 5-3=2 and 2 is not in the set

the set is not closed under division

example:3/5=3/5 and 3/5 is not in the set

the set is closed under multiplication because if you multiply any two elements of the set (odd integers) you get an odd integer (odd times odd equals odd; positive or negative)