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 A036552 List of pairs (m,2m) where m is the least unused positive number. 5
 1, 2, 3, 6, 4, 8, 5, 10, 7, 14, 9, 18, 11, 22, 12, 24, 13, 26, 15, 30, 16, 32, 17, 34, 19, 38, 20, 40, 21, 42, 23, 46, 25, 50, 27, 54, 28, 56, 29, 58, 31, 62, 33, 66, 35, 70, 36, 72, 37, 74, 39, 78, 41, 82, 43, 86, 44, 88, 45, 90, 47, 94, 48, 96, 49, 98, 51, 102 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A permutation of the natural numbers. Inverse permutation is A065037. LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 P. Erdős, R. Freud, and N. Hegyvári, Arithmetical properties of permutations of integers, Acta Mathematica Hungarica 41:1-2 (1983), pp 169-176. MATHEMATICA w = {}; Do[ w = If[ FreeQ[w, k], w = Join[w, {k, 2k}], w], {k, 100}]; w (* Jean-François Alcover, Nov 04 2011, after Wouter Meeussen *) PROG (Haskell) import Data.List (delete) a036552 n = a036552_list !! (n-1) a036552_list = g [1..] where    g (x:xs) = x : (2*x) : (g \$ delete (2*x) xs) -- Reinhard Zumkeller, Feb 07 2011 CROSSREFS Alternating merge of A003159 and A036554. Cf. A064736, A065037. Sequence in context: A082332 A154285 A258078 * A257987 A132169 A273666 Adjacent sequences:  A036549 A036550 A036551 * A036553 A036554 A036555 KEYWORD nonn,easy,nice AUTHOR STATUS approved

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Last modified October 16 09:29 EDT 2019. Contains 328056 sequences. (Running on oeis4.)