

A064418


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(n1) } >= 4.


3



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
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OFFSET

1,2


COMMENTS

A permutation of the natural numbers.


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), 437446.
Index entries for sequences related to EKG sequence
Index entries for sequences that are permutations of the natural numbers


MATHEMATICA

A064418 = Range[4]; Do[ For[ an=5, True, an++, If[GCD[an, Last[A064418]] >= 4 && FreeQ[A064418, an], AppendTo[A064418, an]; Break[]]], {70}]; A064418 (* JeanFrançois Alcover, May 07 2012 *)


PROG

(Haskell)
import Data.List (delete)
a064418 n = a064418_list !! (n1)
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


CROSSREFS

Cf. A064413. Inverse permutation: A064958.
Sequence in context: A245388 A164573 A004045 * A171164 A283659 A032939
Adjacent sequences: A064415 A064416 A064417 * A064419 A064420 A064421


KEYWORD

nonn,nice,easy


AUTHOR

Jonathan Ayres (Jonathan.ayres(AT)btinternet.com), Sep 30 2001


EXTENSIONS

More terms from Naohiro Nomoto, Sep 30 2001


STATUS

approved



