login
This site is supported by donations to The OEIS Foundation.

 

Logo

"Email this user" was broken Aug 14 to 9am Aug 16. If you sent someone a message in this period, please send it again.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A004147 Number of n-state Turing machines which halt.
(Formerly M5233)
3
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

M. Somos, Busy Beaver Turing Machine

M. 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified August 17 23:58 EDT 2017. Contains 290682 sequences.