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 A064421 Term at which n appears in A064413 (if it begins at 2). 13
 0, 1, 4, 2, 9, 3, 13, 7, 5, 8, 19, 6, 27, 12, 10, 16, 32, 11, 36, 17, 14, 18, 42, 15, 23, 26, 21, 25, 56, 22, 60, 30, 20, 31, 24, 29, 66, 35, 28, 39, 73, 34, 80, 40, 38, 41, 88, 44, 49, 45, 33, 46, 99, 47, 52, 48, 37, 55, 106, 51, 114, 59, 50, 63, 53, 58, 127, 64, 43, 54, 133 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Every nonnegative number appears here exactly once. LINKS J. C. Lagarias, E. M. Rains and N. J. A. Sloane, The EKG sequence, Exper. Math. 11 (2002), 437-446. MATHEMATICA terms = 100; ekg[s_] := Block[{m = s[[-1]], k = 3}, While[MemberQ[s, k] || GCD[m, k] == 1, k++]; Append[s, k]]; EKG = Nest[ekg, {2, 4}, 2 terms]; a[1] = 0; a[n_] := FirstPosition[EKG, n] // First; Array[a, terms] (* Jean-François Alcover, Aug 30 2018, after Robert G. Wilson v *) CROSSREFS Cf. A064413. Equals A064664 - 1. Sequence in context: A060734 A075594 A076022 * A051494 A262025 A118013 Adjacent sequences:  A064418 A064419 A064420 * A064422 A064423 A064424 KEYWORD nonn AUTHOR Jonathan Ayres (Jonathan.ayres(AT)btinternet.com), Sep 30 2001 EXTENSIONS More terms from Naohiro Nomoto, Sep 30 2001 STATUS approved

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Last modified August 12 12:09 EDT 2020. Contains 336439 sequences. (Running on oeis4.)