A251546 a(n) = smallest even number not in {A098550(1), A098550(2), ..., A098550(n)}.

2, 4, 4, 6, 6, 6, 6, 6, 6, 10, 10, 10, 10, 10, 10, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 24, 24, 30, 30, 30, 30, 30, 30, 38, 38, 40, 40, 40, 40, 40, 40, 40, 46, 46, 46, 46, 46, 46, 46, 46, 54, 54, 54

Offset

1,1

Comments

A251416(n) = Min{a(n), A251549(n)}. - Reinhard Zumkeller, Dec 19 2014

Links

Chai Wah Wu, 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 [math.NT], 2015 and J. Int. Seq. 18 (2015) 15.6.7.

Mathematica

terms = 100;
f[lst_List] := 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}, terms - 3];
a[1] = 2;
a[n_] := a[n] = For[k = a[n-1], True, k += 2, If[FreeQ[A098550[[1;; n]], k], Return[k]]];
Array[a, terms] (* Jean-François Alcover, Aug 01 2018, after Robert G. Wilson v *)

Prog

(Haskell)
import Data.List ((\\))
a251546 n = head $ [2, 4 ..] \\ filter even (take n a098550_list)
-- Reinhard Zumkeller, Dec 19 2014

Crossrefs

Cf. A098550, A247253, A251416, A251417, A251547, A251548, A251549, A251550, A251551, A251552.

See also A251557, A251558, A251559.

Sequence in context: A340226 A348769 A058043 * A282894 A162550 A191682

Adjacent sequences: A251543 A251544 A251545 * A251547 A251548 A251549

Keyword

nonn

Author

N. J. A. Sloane, Dec 18 2014

Status

approved