a) 19 a, unde a = 3". 5n+2+3n+2.5n-3n+1.5n+1;
b) 391a, unde a = 5n . 7+2 + 5n+2.7n_5n+1.7m+1;
c) 13|a, unde a = 3n+3. 22n + 3n+1. 22n+4 - 3n+2. 22n+2;
d) 13|a, unde a = 5". 4n+3 +5+1. 4n+2 + 5n+1. 4n5n+2. 4n+1. BE
e) 29 | a, unde a=23n+1.5n+3 + 8n+2. 5n+2-23n+2. 5n+1.72.