n=numarul cautat !
conform ipotezei 100 ≤ n ≤ 999 => n=M₃₇ + 9 adica: n-9 = M₃₇
100 : 37 ≈ 2,7... adica n - 9 ≥ 120 ;
si 999 : 37 ≈ 26 ... ,, n - 9 ≤ 962 ;
avem n = {3*37+9=120; 4*37+9=157; 5*37+9=194; ... ; 26*37+9=971}
in total avem 26-3+1 =24 numere , suma acestora va fi:
S = 120 + 157 + 194 + ... + 971=
= 120 +120+1*37 + 120+2*37 + ... + 120+23*37 =
= 24*120 + 37(1+2+3+...+23)=2880+37*(23*24/2)=
= 2880 + 10212 = 13092
