int gcd(int a, int b) {
    int t;
    while(b > 0) {
        t = a;
        a = b;
        b = t % b;
    }

    return a < 0 ? -a : a;
}

size(10cm,10cm);

int ndots = 6;
draw((0,0)--(ndots - 0.5,0),Arrow);
draw((0,0)--(0,ndots - 0.5),Arrow);

for(int i = 1; i < ndots; ++i) {
    for(int j = 1; j < ndots; ++j) {
        //Loop needed to ensure lines go behind all other objects
        pair tree = (i, j);
        if (gcd(i,j) == 1 ) {
            draw((0,0)--tree,dotted);
        }
    }
}

for(int i = 1; i < ndots; ++i) {
    for(int j = 1; j < ndots; ++j) {
        pair tree = (i, j);
        path circ = circle(tree, 0.04);

        if(gcd(i, j) == 1) {
            draw(circ, heavyblue);
            fill(circ, heavyblue);
        } else {
            draw(circ, heavyred);
            fill(circ, heavyred);
        }

        label("$\frac{"+string(i)+"}{"+string(i+j)+"}$", tree, NE);

    }
}