In 1964 (only 2 years after Tibor Radó first described the Busy Beaver game), Milton W. Green of the Stanford Research Institute hand-crafted a family of fast-growing Turing Machines with \(n\) states, 2 symbols for all \(n \ge 4\).1 At the time of publication, Green’s Machines were the Busy Beaver champions for \(BB(n)\) for all \(n \ge 6\). This family grows roughly as fast as the Ackermann function Milton W. Green. “A Lower Bound on Rado’s Sigma Function for Binary Turing Machines...
