A169849 - OEIS

%I #7 May 16 2019 01:32:32

%S 9,3,6,2,4,8,10,5,15,12,14,7,21,18,16,20,22,11,33,24,26,13,39,27,30,

%T 25,35,28,32,34,17,51,36,38,19,57,42,40,44,46,23,69,45,48,50,52,54,56,

%U 49,63,60,55,65,70,58,29,87,66,62,31,93,72,64,68,74,37,111,75,78,76,80,82,41

%N EKG sequence started at 9 instead of 2.

%C A generalization of A064413.

%C a(n) = A064413(n+1) for n > 43; a(n) = A169837(n) for n > 9. - _Reinhard Zumkeller_, Jul 04 2014

%H Reinhard Zumkeller, <a href="/A169849/b169849.txt">Table of n, a(n) for n = 1..10000</a>

%H Gordon Hamilton, <a href="http://www.youtube.com/watch?v=yd2jr30K2R4">The EKG Sequence and the Tree of Numbers</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/EKGSequence.html">EKG Sequence</a>

%H <a href="/index/Ed#EKG">Index entries for sequences related to EKG sequence</a>

%o (Haskell)

%o import Data.List (delete)

%o a169849 n = a169849_list !! (n-1)

%o a169849_list = 9 : ekg 9 (delete 9 [2..]) where

%o    ekg x zs = f zs where

%o        f (y:ys) = if gcd x y > 1 then y : ekg y (delete y zs) else f ys

%o -- _Reinhard Zumkeller_, Jul 04 2014

%Y  Cf. A064413, A064417, A169837.

%K nonn

%O 1,1

%A _T. D. Noe_ and _N. J. A. Sloane_, Jun 02 2010