User:Wythagoras/Rado's sigma function/BB(4)

\(\Sigma(4)=13\) (Brady, 1974).

The following machine gives this result: 0 _ 1 r 1 0 1 1 l 2 1 _ 1 l 0 1 1 1 r 1 2 _ 1 l 1 2 1 1 r halt