Explicație pas cu pas:
S(1)=14+21+...+700
14+7(n-1)=700=>n=(700-7)/7=>n=99
S(1)=[(700+14)/2]*99=35343
sau:
S(1)=7(2+3+...+100)=7*[99*(100+2)/2]=7*51*99=35343
