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 A098311 Smallest number not occurring earlier and coprime to a(ceiling(n/2)); a(1)=1. 4

%I

%S 1,2,3,5,4,7,6,8,9,11,10,12,13,17,15,19,14,16,18,20,21,23,25,29,22,24,

%T 26,27,28,31,30,32,33,37,35,39,41,43,47,49,34,38,36,40,42,44,45,46,51,

%U 53,55,59,57,61,50,52,65,67,48,54,71,73,63,69,56,58,60,62,64,66,68,70

%N Smallest number not occurring earlier and coprime to a(ceiling(n/2)); a(1)=1.

%C a(2*n) > a(2*n-1);

%C permutation of the natural numbers with inverse A098313:

%C A098312(n) = a(a(n)).

%H Reinhard Zumkeller, <a href="/A098311/b098311.txt">Table of n, a(n) for n = 1..10000</a>

%H <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>

%o import Data.List ((\\))

%o a098311 n = a098311_list !! (n-1)

%o a098311_list = 1 : ys where

%o ys = 2 : f ys [3..] where

%o f (v:vs) ws = us ++ f vs (ws \\ us) where

%o us = take 2 \$ filter ((== 1) . (gcd v)) ws

%o -- _Reinhard Zumkeller_, Oct 11 2014

%K nonn

%O 1,2

%A _Reinhard Zumkeller_, Sep 02 2004

%E Typo in definition fixed by _Reinhard Zumkeller_, Oct 11 2014

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Last modified August 3 14:40 EDT 2021. Contains 346438 sequences. (Running on oeis4.)