1. b = 0 a ∈ {0,1,2,3,4,5,6,7,8,9} sunt 10 numere
2. b ∈ {0,2,4,6,8}
ptr. b = 0 a ∈{3,6,9} 3 numere
ptr. b = 2 a∈ {4,7} 2 numere
b = 4 a∈ {2,5,8} 3 numere
b = 6 a∈ {0,3,6,9,} 4 numere
b = 8 a ∈ {1,4,7,} 3 numere total : 15 numere∈
3. 4a6b b ∈ (0,2,4,6,8} 9 | (4 +6 + a + b) 9 | (10 + a + b) ⇒
⇒ a + b = 8 a ∈ {8 ,6,4,2,0} de ex : 4860, 4662...
4. 8a9b = 5x + 1 8a9b - 1 = 5x ⇒ b∈{1,6} a ∈ {0,1,2,3....9}
5. 77ab ⇒ ab ∈ {00,11,22,33,44,55,66,77,88,99} ⇒ a = b
6. 1339ab ab ∈ {00,13,26,39,52,65,78,91}
7. 28ab14 ab ∈ {00,14,28,42,56,70,84,98}
