A251414 a(n) = (A251413(n) + 1)/2.

1, 2, 3, 5, 13, 11, 28, 4, 6, 18, 17, 25, 8, 39, 14, 46, 23, 7, 26, 33, 9, 20, 43, 29, 58, 10, 12, 48, 35, 63, 32, 73, 41, 15, 38, 102, 47, 60, 16, 53, 171, 44, 61, 56, 72, 19, 50, 93, 59, 78, 62, 88, 21, 67, 103, 74, 108, 71, 22, 24, 65, 118, 77, 123, 80, 81

Offset: 1

Author

N. J. A. Sloane, Dec 02 2014

Keywords

• nonn

Comments

Conjectured to be a permutation of the natural numbers.

References

• L. Edson Jeffery, Posting to Sequence Fans Mailing List, Dec 01 2014

Links

• N. J. A. Sloane, Table of n, a(n) for n = 1..11945
• 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.

Crossrefs

Cf. A098550, A251413.

Programs

Mathematica

max = 57; f = True; a = {1, 3, 5}; NN = Range[4, 1000]; s = 2*NN - 1; While[TrueQ[f], For[k = 1, k <= Length[s], k++, If[Length[a] < max, If[GCD[a[[-1]], s[[k]]] == 1 && GCD[a[[-2]], s[[k]]] > 1, a = Append[a, s[[k]]]; s = Delete[s, k]; k = 0; Break], f = False]]]; Table[(a[[n]] + 1)/2, {n, max}] (* L. Edson Jeffery, Dec 02 2014 *)

Python

from _future_ import division
from math import gcd
A251414_list, l1, l2, s, b = [1,2,3], 5, 3, 7, {}
for _ in range(1,10**2):
    i = s
    while True:
        if not i in b and gcd(i,l1) == 1 and gcd(i,l2) > 1:
            A251414_list.append((i+1)//2)
            l2, l1, b[i] = l1, i, True
            while s in b:
                b.pop(s)
                s += 2
            break
        i += 2 # Chai Wah Wu, Dec 07 2014