

A039634


Fixed point of "n > n/2 or (n1)/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
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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. A039635A039645, 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



