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 A251604 A Zumkeller-type sequence (cf. A098550): a(n) = n if n <= 3, otherwise the smallest number not occurring earlier having at least one common factor with a(n-2)+a(n-1), but none with a(n-1). 6
 1, 2, 3, 5, 4, 9, 13, 6, 19, 10, 29, 12, 41, 53, 8, 61, 15, 14, 87, 101, 16, 21, 37, 18, 11, 58, 23, 24, 47, 71, 20, 7, 27, 17, 22, 39, 122, 35, 157, 26, 33, 59, 28, 45, 73, 30, 103, 38, 51, 89, 25, 32, 57, 178, 55, 233, 34, 63, 97, 36, 49, 40, 267, 307, 42 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Conjectured to be a permutation of the positive integers. See also A255972 for this conjecture. - Reinhard Zumkeller, Mar 12 2015 LINKS Peter J. C. Moses, Table of n, a(n) for n = 1..5000 David L. Applegate, Hans Havermann, Bob Selcoe, Vladimir Shevelev, N. J. A. Sloane, and Reinhard Zumkeller, The Yellowstone Permutation, arXiv preprint arXiv:1501.01669 [math.NT], 2015 and J. Int. Seq. 18 (2015) 15.6.7. MATHEMATICA a[n_] := a[n] = If[n <= 3, n, For[k = 1, True, k++, If[FreeQ[Array[a, n-1], k], If[!CoprimeQ[k, a[n-2]+a[n-1]] && CoprimeQ[k, a[n-1]], Return[k]]]]]; Array[a, 65] (* Jean-François Alcover, Jul 31 2018 *) PROG (Haskell) import Data.List (delete) a251604 n = a251604_list !! (n-1) a251604_list = 1 : 2 : 3 : f 2 3 [4..] where    f u v ws = g ws where      g (x:xs) = if gcd x (u + v) > 1 && gcd x v == 1                    then x : f v x (delete x ws) else g xs -- Reinhard Zumkeller, Mar 12 2015 CROSSREFS Cf. A098550. Cf. A255972. Sequence in context: A060030 A081025 A245607 * A124653 A085947 A069202 Adjacent sequences:  A251601 A251602 A251603 * A251605 A251606 A251607 KEYWORD nonn AUTHOR Vladimir Shevelev, Dec 13 2014 EXTENSIONS More terms from Peter J. C. Moses, Dec 13 2014 STATUS approved

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Last modified September 19 21:17 EDT 2018. Contains 315217 sequences. (Running on oeis4.)