A251546 - OEIS

%I #27 Aug 01 2018 09:21:18

%S 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,

%T 18,18,18,18,24,24,30,30,30,30,30,30,38,38,40,40,40,40,40,40,40,46,46,

%U 46,46,46,46,46,46,54,54,54

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

%C A251416(n) = Min{a(n), A251549(n)}. - _Reinhard Zumkeller_, Dec 19 2014

%H Chai Wah Wu, <a href="/A251546/b251546.txt">Table of n, a(n) for n = 1..10000</a>

%H David L. Applegate, Hans Havermann, Bob Selcoe, Vladimir Shevelev, N. J. A. Sloane, and Reinhard Zumkeller, <a href="http://arxiv.org/abs/1501.01669">The Yellowstone Permutation</a>, arXiv preprint arXiv:1501.01669 [math.NT], 2015 and <a href="https://cs.uwaterloo.ca/journals/JIS/VOL18/Sloane/sloane9.html">J. Int. Seq. 18 (2015) 15.6.7</a>.

%t terms = 100;

%t f[lst_List] := Block[{k = 4}, While[GCD[lst[[-2]], k] == 1 || GCD[lst[[-1]], k] > 1 || MemberQ[lst, k], k++]; Append[lst, k]];

%t A098550 = Nest[f, {1, 2, 3}, terms - 3];

%t a[1] = 2;

%t a[n_] := a[n] = For[k = a[n-1], True, k += 2, If[FreeQ[A098550[[1;;n]], k], Return[k]]];

%t Array[a, terms] (* _Jean-François Alcover_, Aug 01 2018, after _Robert G. Wilson v_ *)

%o (Haskell)

%o import Data.List ((\\))

%o a251546 n = head $ [2, 4 ..] \\ filter even (take n a098550_list)

%o -- _Reinhard Zumkeller_, Dec 19 2014

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

%Y See also A251557, A251558, A251559.

%K nonn

%O 1,1

%A _N. J. A. Sloane_, Dec 18 2014