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%I #27 Oct 08 2020 03:56:55
%S 1,16,4096,2985984,4294967296,10240000000000,36520347436056576,
%T 182059119829942534144,1208925819614629174706176,
%U 10314424798490535546171949056,109951162777600000000000000000000,1432052311740255546466984939315265536
%N Number of n-state 2-symbol halt-free Turing machines.
%C A Turing machine is halt-free if none of its instructions lead to the halt state.
%C This sequence is strictly less than A052200(n) for all n > 0, since halt-free n-state machines are a strict subset of all n-state machines.
%C Solutions to the so-called "Beeping Busy Beaver" problem will almost certainly be halt-free programs.
%H Scott Aaronson, <a href="https://www.scottaaronson.com/papers/bb.pdf">The Busy Beaver Frontier</a>.
%H Nick Drozd, <a href="https://nickdrozd.github.io/2020/08/13/beeping-busy-beavers.html">Beeping Busy Beavers</a>.
%F a(n) = ((4*n)^2)^n.
%o (Python) [((4 * n) ** 2) ** n for n in range(12)]
%Y Cf. A052200.
%K nonn,easy
%O 0,2
%A _Nicholas Drozd_, Aug 11 2020
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