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

Author

Reinhard Zumkeller, Dec 02 2014

Keywords

• nonn

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.

Crossrefs

Cf. A098550, A005843, A251238, A251393.

First row of array A251716.

Programs

Haskell

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

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 *)