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A064417
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a(1) = 1, a(2) = 2, a(3) = 3; for n >3 a(n) = smallest number not already used such that GCD{ a(n), a(n-1) } >= 3.
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3
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1, 2, 3, 6, 9, 12, 4, 8, 16, 20, 5, 10, 15, 18, 21, 7, 14, 28, 24, 27, 30, 25, 35, 40, 32, 36, 33, 11, 22, 44, 48, 39, 13, 26, 52, 56, 42, 45, 50, 55, 60, 51, 17, 34, 68, 64, 72, 54, 57, 19, 38, 76, 80, 65, 70, 49, 63, 66, 69, 23, 46, 92, 84, 75, 78, 81, 87, 29, 58, 116, 88, 77, 91
(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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REFERENCES
| J. C. Lagarias, E. M. Rains and N. J. A. Sloane, Problem 10927, Amer. Math. Monthly, 109 (2002), 202; 111 (No. 2, 2004), 167-168.
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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)
a064417 n = a064417_list !! (n-1)
a064417_list = 1 : 2 : 3 : f 3 [4..] where
f x us = x' : f x' (delete x' us) where
x' = head [u | u <- us, gcd u x > 2]
-- Reinhard Zumkeller, Nov 13 2011
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CROSSREFS
| Cf. A064413. A064956 gives inverse permutation.
Sequence in context: A032704 A029805 A082007 * A191981 A131975 A057474
Adjacent sequences: A064414 A064415 A064416 * A064418 A064419 A064420
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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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