A251546 - OEIS

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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

(list; graph; refs; listen; history; text; internal format)

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.