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%I #10 Aug 24 2015 02:26:19
%S 2,3,5,11,7,17,13,41,19,67,23,83,29,109,31,127,37,157,43,191,47,211,
%T 53,241,59,277,61,283,71,353,73,367,79,401,89,461,97,509,101,547,103,
%U 563,107,587,113,617,131,739,137,773,139,797,149,859,151,877,163,967,167
%N a(2n-1) = the smallest prime not occurring earlier in the sequence. a(2n) = the a(2n-1)th prime.
%C This sequence is a permutation of the primes.
%e The smallest prime not occurring among the first 8 terms of the sequence is 19; So a(9) = 19. The a(9)th prime = 19th prime is 67; so a(10) = 67.
%p A131200 := proc(nmax) local a,i,n; a := [2] ; for n from 2 to nmax do if n mod 2 = 0 then a := [op(a),ithprime(op(-1,a))] ; else for i from 1 do if not ithprime(i) in a then a := [op(a),ithprime(i)] ; break ; fi ; od; fi ; od; a ; end: A131200(80); # _R. J. Mathar_, Oct 30 2007
%t a = {}; For[n = 1, n < 65, n++, If[OddQ[n], i = 1; While[Length[Intersection[{Prime[i]}, a]] > 0, i++ ]; AppendTo[a, Prime[i]], AppendTo[a, Prime[a[[ -1]]]]]]; a (* _Stefan Steinerberger_, Oct 27 2007 *)
%K nonn
%O 1,1
%A _Leroy Quet_, Oct 21 2007
%E More terms from _Stefan Steinerberger_ and _R. J. Mathar_, Oct 27 2007
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