According to the theory of multi-warhead attacking surface target, when three clustered 300,000-ton warheads are distributed in a regular triangle with a side length of 30 kilometers (it seems that the distance is not clear), the damage effect of hollow blasting on an unprotected urban target with ground obstacles is equivalent to that of a 2 million-ton warhead. This is the data I saw from weapons knowledge a year or two ago. Generally speaking, the attack on such targets as cities mainly plays a deterrent role, that is, it causes casualties and scares opponents, and there is no need to exterminate civilians. Generally speaking, 2 million tons is enough. The theory that multiple nuclear bombs hit the same target (in this case, the target refers to a vast area) has never appeared except for the nuclear strike against the rival nuclear bomb silo during the Cold War. The Soviet Union once had three 100-million-ton-equivalent nuclear bombs to destroy the abnormal theory of a medium-sized country and conducted experiments, but they were never installed. You should know by searching "Khrushchev Nuclear Bomb".