D=7+7^(2)+7^(3)+................+7^(2004) =
avem 2004 termeni putem sa ii grupam cate 3 (2004:3)=668 grupuri
=7*[1+7^(1)+7^(2)]+................+7^2002(1+7^(1)+7^(2)] =
=(1+7+49)+................+7^2002(1+7+49) =
=57*(7+................+7^2002) se divide cu 57