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A064418
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a(1) = 1, a(2) = 2, a(3) = 3, a(4) = 4; for n > 4, a(n) = smallest number not already used such that GCD{ a(n), a(n-1) } >= 4.
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3
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1, 2, 3, 4, 8, 12, 6, 18, 9, 27, 36, 16, 20, 5, 10, 15, 25, 30, 24, 28, 7, 14, 21, 35, 40, 32, 44, 11, 22, 33, 55, 45, 50, 60, 42, 48, 52, 13, 26, 39, 65, 70, 49, 56, 63, 54, 66, 72, 64, 68, 17, 34, 51, 85, 75, 80, 76, 19, 38, 57, 95, 90, 78, 84, 77, 88, 92, 23, 46, 69, 115, 100, 96
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| A permutation of the natural numbers.
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LINKS
| Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
J. C. Lagarias, E. M. Rains and N. J. A. Sloane, The EKG sequence, Exper. Math. 11 (2002), 437-446.
Index entries for sequences related to EKG sequence
Index entries for sequences that are permutations of the natural numbers
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PROG
| (Haskell)
import Data.List (delete)
a064418 n = a064418_list !! (n-1)
a064418_list = 1 : 2 : 3 : 4 : (f 4 [5..]) where
f :: Integer -> [Integer] -> [Integer]
f x xs = m : (f m $ delete m xs) where
m = head $ dropWhile ((< 4) . (gcd x)) xs
-- Reinhard Zumkeller, Feb 20 2011
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CROSSREFS
| Cf. A064413. Inverse permutation: A064958.
Sequence in context: A046812 A164573 A004045 * A171164 A032939 A030073
Adjacent sequences: A064415 A064416 A064417 * A064419 A064420 A064421
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KEYWORD
| nonn,nice,easy
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AUTHOR
| Jonathan Ayres (Jonathan.ayres(AT)btinternet.com), Sep 30 2001
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EXTENSIONS
| More terms from Naohiro Nomoto (n_nomoto(AT)yabumi.com), Sep 30 2001
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