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

Author

N. J. A. Sloane, Dec 18 2014

Keywords

• nonn

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.

Crossrefs

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

See also A251557, A251558, A251559.

Programs

Haskell

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

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 *)