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

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A121056 From a puzzle of Roger Penrose's in the Twistor Newsletter. 3
7, 9, 12, 16, 24, 36, 56, 90 (list; graph; refs; listen; history; internal format)
OFFSET

-3,1

COMMENTS

Roger Penrose posed the problem of finding the missing term in the sequence "..., 7, 9, 12, ?, 24, 36, 56, 90, ...".

The answer is that the sequence is given by a(n) = 24*(2^n-1)/n, for n = -3, -2, ..., 3, 4 and so the missing entry is (by l'Hopital's rule) 24 log 2 = 16.6355323... [This has been replaced by 16 here to get an integer sequence.]

The sequence for n = -10, ..., 10 is 3069/1280, 511/192, 765/256, 381/112, 63/16, 93/20, 45/8, 7, 9, 12, 24 log 2, 24, 36, 56, 90, 744/5, 252, 3048/7, 765, 4088/3, 12276/5.

REFERENCES

Roger Penrose, Twistor Newsletter, No. 10 (1980), p. 22.

CROSSREFS

Cf. A003138, A003176, A003177.

Sequence in context: A075335 A020720 A048589 * A174189 A112529 A161892

Adjacent sequences:  A121053 A121054 A121055 * A121057 A121058 A121059

KEYWORD

nonn

AUTHOR

N. J. A. Sloane (njas(AT)research.att.com), Aug 10 2006

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

Content is available under The OEIS End-User License Agreement .

Last modified February 14 14:47 EST 2012. Contains 205623 sequences.