login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A039634 Fixed point of "n -> n/2 or (n-1)/2 until result is prime". 16
1, 2, 3, 2, 5, 3, 7, 2, 2, 5, 11, 3, 13, 7, 7, 2, 17, 2, 19, 5, 5, 11, 23, 3, 3, 13, 13, 7, 29, 7, 31, 2, 2, 17, 17, 2, 37, 19, 19, 5, 41, 5, 43, 11, 11, 23, 47, 3, 3, 3, 3, 13, 53, 13, 13, 7, 7, 29, 59, 7, 61, 31, 31, 2, 2, 2, 67, 17, 17, 17, 71, 2, 73, 37, 37, 19, 19, 19, 79, 5, 5 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) is the largest prime whose binary expansion is an initial substring of n's binary expansion. - Charlie Neder, Oct 27 2018

a(1) = 1 by convention. - David A. Corneth, Oct 27 2018

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

MATHEMATICA

ner[ n_Integer ] := FixedPoint[ If[ EvenQ[ # ]&&#>2, #/2, If[ PrimeQ[ # ]||(#=== 1), #, (#-1)/2 ] ]&, n, 20 ]

PROG

(Haskell)

a039634 1 = 1

a039634 n = until ((== 1) . a010051) (flip div 2) n

-- Reinhard Zumkeller, Nov 17 2013

(PARI) a(n)=while(n>3 && !isprime(n), n\=2); n \\ Charles R Greathouse IV, Jun 23 2017

CROSSREFS

Cf. A039635-A039645, A010051, A039636, A039638, A039639.

Sequence in context: A097975 A130088 A078834 * A078833 A210437 A109674

Adjacent sequences:  A039631 A039632 A039633 * A039635 A039636 A039637

KEYWORD

nonn,easy,nice

AUTHOR

Wouter Meeussen

EXTENSIONS

Offset corrected by Reinhard Zumkeller, Nov 17 2013

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
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 22 10:29 EDT 2021. Contains 348160 sequences. (Running on oeis4.)