j=2: n=16 m=25  P(K<=1) in [0.033129, 0.033258]  (Chernoff bound 1.651e-01)
j=3: n=81 m=109  P(K<=1) in [0.002241, 0.002356]  (Chernoff bound 1.646e-02)
j=4: n=256 m=321  P(K<=1) in [0.000053, 0.000074]  (Chernoff bound 5.938e-04)
sum over j=5..399 of 2*Chernoff bound = 1.575e-05; j>=400 negligible (Cantelli c_k<=3/j^2 would give <=0.015, Chernoff decays much faster)
NUMERIC: P(|G|=2) in [0.4444, 0.4446] ; hence P(|G|=4) approx 0.5554..0.5556
