I need to prove this question: 2 the set of all even natural numbers. Prove that 2 is countably infinite.

I know that I can combine each even number with an number so that 2=1, 4=2, 6=3,....

={1,2,3,4,5,6,.....,n} (n∈ )

2={2,4,6,8,10,12,...2n} (n∈ )

I know how to write it down but not how to prove it proper.

And ik know I need to prove its bijective but I dont know how.