A251237 Indices of even numbers in A098550.

2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 25, 27, 29, 31, 33, 35, 37, 39, 41, 44, 46, 48, 50, 52, 54, 56, 58, 60, 63, 65, 67, 69, 71, 73, 75, 77, 80, 82, 84, 86, 89, 91, 93, 95, 97, 99, 102, 104, 106, 108, 110, 112, 115, 117, 119, 121, 123, 125, 128, 130, 133, 135

Offset

1,1

Comments

A098550(a(n)) mod 2 = 0;

a(n+1) > a(n) + 1;

there are infinitely many even terms in A098550, for proof: see comment #4 in A098550.

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

f[lst_] := Block[{k = 4}, While[GCD[lst[[-2]], k] == 1 || GCD[lst[[-1]], k] > 1 || MemberQ[lst, k], k++]; Append[lst, k]];
Position[Nest[f, {1, 2, 3}, 140], _?EvenQ] // Flatten (* Jean-François Alcover, Oct 01 2018, after Robert G. Wilson v in A098550 *)

Prog

(Haskell)
a251237 n = a251237_list !! (n-1)
a251237_list = filter (even . a098550) [1..]

Crossrefs

Cf. A098550, A005843, A251238, A251393.

First row of array A251716.

Sequence in context: A272670 A234521 A085125 * A194402 A134930 A084562

Adjacent sequences: A251234 A251235 A251236 * A251238 A251239 A251240

Keyword

nonn

Author

Reinhard Zumkeller, Dec 02 2014

Status

approved