a/n=b/m=c/p=d/q=7,m,n,p,q≠0
(a+b)/(n+m)=(b+c)/(m+p)=(c+d)/(p+q)=(d+a)/(q+n)=7
=>[(2a+2b+2c+2d)/(2n+2m+2p+2q)]-17=7*4-17=28-17=11
si 7^2 -[(a+b+c+d)/(n+m+p+q)]=49-(7*4:4)=49-(28:4)=49-7=42
a;b;c;d pot fi { 7;14;21;28;35;42;49....etc] => nr. divizibile cu 7
n;m;p;q pot fi {1;2;3;4;5;6;7...etc }≠0
