A251411 Numbers k such that A098550(k) = k.

1, 2, 3, 4, 12, 50, 86

Offset

1,2

Comments

There is a strong conjecture that there are no further terms. See the discussion in the comments in A098550.

References

L. Edson Jeffery, Posting to Sequence Fans Mailing List, Nov 30 2014.

Links

Table of n, a(n) for n=1..7.

Hans Havermann, Loops and unresolved chains for map n -> A098550(n) trajectories

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

max = 100;
f[lst_] := 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}, max - 3];
Select[Transpose[{Range[max], A098550}], #[[1]] == #[[2]]&][[All, 1]] (* Jean-François Alcover, Sep 05 2018, after Robert G. Wilson v in A098550 *)

Prog

(Python)
from math import gcd
A251411_list, l1, l2, s, b = [1, 2, 3], 3, 2, 4, {}
for n in range(4, 10**4):
    i = s
    while True:
        if not i in b and gcd(i, l1) == 1 and gcd(i, l2) > 1:
            l2, l1, b[i] = l1, i, 1
            while s in b:
                b.pop(s)
                s += 1
            if i == n:
                A251411_list.append(n)
            break
        i += 1 # Chai Wah Wu, Dec 03 2014

Crossrefs

Cf. A098550, A251412, A251556.

Sequence in context: A165302 A276530 A360061 * A117342 A328210 A303385

Adjacent sequences: A251408 A251409 A251410 * A251412 A251413 A251414

Keyword

nonn,more

Author

N. J. A. Sloane, Dec 02 2014

Status

approved