Nu înțeleg , mulțumesc!!!

[tex]\it 1=1+6\cdot0\\ 7=1+6\cdot1\\ 13=1+6\cdot2\\.\\.\\.\\109=1+6\cdot18\\ \rule{70}{0.3}\\S=1\cdot19+6(1+2+...+18) =19+6\cdot\dfrac{18\cdot19}{2}=19(1+3\cdot18)=1045[/tex]