A={13,14,15,..,73}
B={ab|ab=ba}
ab=ba => a=b => a,b∈{1,2,3,4,5,6,7,8,9}
............................ab,ba∈{11,22,33,44,55,66,77,88,99}
B={11,22,33,44,55,66,77,88,99}
A∩B={22,33,44,55,66}
Observatii: -ab sau ba trebuie scris cu bara deasupra
-a si b ∉ N ,a si b ∈N* pentru ca nu exista nr 00