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A092401
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List of pairs n, 3n, where n is the least unused number so far.
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4
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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
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OFFSET
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1,2
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COMMENTS
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A permutation of the natural numbers.
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LINKS
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FORMULA
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MATHEMATICA
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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 *)
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PROG
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(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
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CROSSREFS
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KEYWORD
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easy,nice,nonn
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AUTHOR
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STATUS
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approved
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