Consider prime numbers from 1 to 100 : (2; 3; 5; 7; ...; 97)

Consider : 100 - 2 = 98 (removed)

100 - 3 = 97 (to choose)

100 - 5 = 95 (removed)

...

So do we get 12 numbers : (97; 3) , (3; 97) , (89; 11) , (11; 89) , (83; 7) , (7; 83) , (71; 29) , (29; 71) , (59; 41) , (41; 59) , (53; 47) , (47; 53)