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%I #13 May 10 2023 23:04:58
%S 2,1,4,3,6,5,8,7,9,11,10,13,12,14,15,17,16,19,18,20,21,23,22,24,25,26,
%T 27,29,28,31,30,32,33,34,35,37,36,38,39,41,40,43,42,44,45,47,46,48,49,
%U 50,51,53,52,54,55,56,57,59,58,61,60,62,63,64,65,67,66,68,69,71,70,73,72
%N Exchange adjacent nonprimes and primes.
%C If we have consecutive numbers, one prime and one nonprime, swap them. So after the initial 2,1,4,3,6,5,8,7 we have "if n is prime, a(n) = n-1; if n+1 is prime, a(n) = n+1, otherwise a(n) = n".
%H Stefano Spezia, <a href="/A167419/b167419.txt">Table of n, a(n) for n = 1..10000</a>
%t a[n_]:=If[PrimeQ[n],n-1,If[PrimeQ[n+1],n+1,n]]; Join[{2,1,4,3,6,5,8,7},Array[a,65,9]] (* _Stefano Spezia_, May 05 2023 *)
%Y Cf. A014681.
%K easy,nonn
%O 1,1
%A _Giovanni Teofilatto_, Nov 03 2009
%E Edited by _Franklin T. Adams-Watters_, Nov 04 2009
%E 42 and 64 inserted by _Stefano Spezia_, May 05 2023
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