A004147 - OEIS

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A004147

Number of n-state Turing machines which halt.
(Formerly M5233)

32, 9784, 7571840, 11140566368

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

This sequence is noncomputable, because it could be used to solve the halting problem. In fact, it is of the same degree of difficulty as the halting problem. - David Diamondstone (skeptical.scientist(AT)gmail.com), Dec 28 2007

REFERENCES

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

Table of n, a(n) for n=1..4.

J. P. Jones, Recursive undecidability - an exposition, Amer. Math. Monthly, 81 (1974), 724-738.

H. Marxen, Busy Beaver

Michael Somos, Busy Beaver Turing Machine

Michael Somos, Busy Beaver

Index entries for sequences related to Busy Beaver problem

CROSSREFS

Cf. A028444, A052200.

Sequence in context: A231035 A213813 A241369 * A212800 A214387 A069444

Adjacent sequences: A004144 A004145 A004146 * A004148 A004149 A004150

KEYWORD

nonn,nice,hard,bref

AUTHOR

N. J. A. Sloane

EXTENSIONS

More terms from David Diamondstone (skeptical.scientist(AT)gmail.com), Dec 28 2007

a(4) from Jonathan Lee, who enumerated all 25.6 billion 4-state machines up to 107 steps, Mar 05 2016

STATUS

approved