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A251558 a(n) = smallest odd number number not in {A098550(1), A098550(2), ..., A098550(n)} which is neither a prime nor a member of A251542. 4
9, 9, 9, 9, 15, 15, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 27, 27, 33, 33, 33, 33, 33, 45, 45, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 57, 57, 57, 57, 57, 57, 57, 69, 69, 75, 75, 75, 75, 75, 75, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 105, 105, 105 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

David L. Applegate, Hans Havermann, Bob Selcoe, Vladimir Shevelev, N. J. A. Sloane, and Reinhard Zumkeller, The Yellowstone Permutation, arXiv preprint arXiv:1501.01669, 2015.

PROG

(Haskell)

import Data.List (delete); import Data.List.Ordered (minus)

a251558 n = a251558_list !! (n-1)

a251558_list = 9 : 9 : 9 : f 2 3 [4..] (tail a014076_list) where

   f u v ws zs = g ws where

     g (x:xs) = if gcd x u > 1 && gcd x v == 1

                   then y : f v x (delete x ws) ys else g xs

                where ys@(y:_) = zs `minus` [x]

-- Reinhard Zumkeller, Mar 11 2015

CROSSREFS

Cf. A098550, A251542, A251546, A251557, A251559.

Cf. A014076.

Sequence in context: A088471 A087416 A216852 * A251559 A068395 A245429

Adjacent sequences:  A251555 A251556 A251557 * A251559 A251560 A251561

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Dec 23 2014

STATUS

approved

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Last modified July 22 22:25 EDT 2017. Contains 289676 sequences.