Leveling Manhattan to the Ground

Manhattan Length = 21.6 km

Explosion Radias = 10.8 km = 10800

10800^3*((27136*1.37895+8649)^(1/2)/13568-93/13568)^2 = 101241082.871 tons = 101.241082871 megatons or 4.184e+17 Joules (Mountain Level)