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 A092401 List of pairs n, 3n, where n is the least unused number so far. 4
 1, 3, 2, 6, 4, 12, 5, 15, 7, 21, 8, 24, 9, 27, 10, 30, 11, 33, 13, 39, 14, 42, 16, 48, 17, 51, 18, 54, 19, 57, 20, 60, 22, 66, 23, 69, 25, 75, 26, 78, 28, 84, 29, 87, 31, 93, 32, 96, 34, 102, 35, 105, 36, 108, 37, 111, 38, 114, 40, 120, 41, 123, 43, 129, 44, 132, 45, 135, 46 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A permutation of the natural numbers. LINKS T. D. Noe, Table of n, a(n) for n=1..1000 FORMULA a(2n-1) = A007417(n), a(2n) = 3*A007417(n). MATHEMATICA A007417 = Select[ Range[100], (# // IntegerDigits[#, 3]& // Split // Last // Count[#, 0]& // EvenQ)&]; a[n_] := If[ OddQ[n], A007417[[(n+1)/2]], 3*A007417[[n/2]] ]; Table[a[n], {n, 1, 100}] (* Jean-François Alcover, Mar 01 2013, from formula *) PROG (Haskell) import Data.List (delete) a092401 n = a092401_list !! (n-1) a092401_list = f [1..] where    f (x:xs) = x : x' : f (delete x' xs) where x' = 3*x -- Reinhard Zumkeller, Jan 03 2012 CROSSREFS Cf. A036552, A203602 (inverse). Sequence in context: A329435 A160795 A258212 * A222208 A302853 A116626 Adjacent sequences:  A092398 A092399 A092400 * A092402 A092403 A092404 KEYWORD easy,nice,nonn AUTHOR Philippe Deléham, Mar 22 2004 STATUS approved

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Last modified February 17 12:32 EST 2020. Contains 331996 sequences. (Running on oeis4.)