intre si intre arata ca nu se iau si marginele intervalului
0<n<200 , dar n∈N, deci n ∈ {1,2,....199} adica in total 199-1+1=199 numere
100<n<200 deci n ∈ {101,102,....199} adica in total 199-101+1=99 numere
100<n<999 deci n apartine{101,102, ....998}. adica in total 998-100+1=898+1=899 numere
