size(0,30cm);

real hydrogenEnergy(int n) {
    return -13.6/(n*n);
}

int width = 5;

label("$E$",(0,0),N);
label("$n$",(width,0),N);


draw((0,hydrogenEnergy(1))--(width,hydrogenEnergy(1)));
for(int i = 2; i <= 30; ++i) {
    draw((0,hydrogenEnergy(i))--(width,hydrogenEnergy(i)),red);
}


label(string(hydrogenEnergy(1)),(0,hydrogenEnergy(1)),W);
label(string(1),(width,hydrogenEnergy(1)),E);

for(int i = 2; i < 7; ++i) {
    label(string(hydrogenEnergy(i),2),(0,hydrogenEnergy(i)),W);
    label(string(i),(width,hydrogenEnergy(i)),E);
}

draw((0,0)--(0,hydrogenEnergy(1)),linewidth(1.2));
draw((width,0)--(width,hydrogenEnergy(1)),linewidth(1.2));