17 points! asap!

i need an example of two numbers that do *not* have a gcf (greatest common factor).

For example like 10 and 3 they dont really have one they both have a gcf of 1

Lets say  your GCF is 20 the ones that would NOT apply are

3,6,7,8,9,11,12,13,14,15,16,17,18,19 because those number can NOT equal up to 20 within a multiple

and these are the ones that do apply 1,2,4,5,10,20  because 1*20=20 2*10=20 4*5=20 5*4=20 10*2=20 20*1=20

Hope this helps if you need a better explanation let me know