Răspuns:
Explicație pas cu pas:
20 = 10 *(1 + 1)
cautam ani de forma abcd care au proprietatea asta ab = 10*(c+b)
1001,1010
2002,2011,2020
3003,3012,3021,3030
4004,4013,4031,4022,4040
5005, 5014,5041,5023,5032,5050
6006,6015,6051,6024,6042,6033,6060
7007,7016,7061,7025,7052,7034,7043,7070
8008,8017,8071,8026,8062,8035,8053,8044,8080
9009,9018,9081,9027,9072,9036,9063,9045,9054,9090
