

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
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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 and J. Int. Seq. 18 (2015) 15.6.7.


MATHEMATICA

terms = 70; max = 2 terms;
f[lst_] := Block[{k = 4}, While[GCD[lst[[2]], k] == 1  GCD[lst[[1]], k] > 1  MemberQ[lst, k], k++]; Append[lst, k]];
A098550 = Nest[f, {1, 2, 3}, max3];
sel = Select[Transpose[{Range[max], A098550}], PrimeQ[#[[2]]]&][[All, 1]]+2;
A251542 = A098550[[sel]]/A098550[[sel2]] ;
a[n_] := For[k = 1, k <= max, k = k+2, If[CompositeQ[k] && FreeQ[A098550[[1 ;; n]], k] && FreeQ[A251542, k], Return[k]]];
Table[a[n], {n, 1, terms}] (* JeanFrançois Alcover, Dec 06 2018, after Robert G. Wilson v in A098550 *)


PROG

(Haskell)
import Data.List (delete); import Data.List.Ordered (minus)
a251558 n = a251558_list !! (n1)
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: A290238 A286833 A216852 * A251559 A068395 A245429
Adjacent sequences: A251555 A251556 A251557 * A251559 A251560 A251561


KEYWORD

nonn


AUTHOR

N. J. A. Sloane, Dec 23 2014


STATUS

approved



