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a(2n-1) = prime(n); a(2n) = least composite number which is coprime to a(2n-1) and which is not already in the sequence.
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%I #5 Dec 05 2013 19:57:05

%S 2,9,3,4,5,6,7,8,11,10,13,12,17,14,19,15,23,16,29,18,31,20,37,21,41,

%T 22,43,24,47,25,53,26,59,27,61,28,67,30,71,32,73,33,79,34,83,35,89,36,

%U 97,38,101,39,103,40,107,42,109,44,113,45,127,46,131,48,137,49,139,50,149

%N a(2n-1) = prime(n); a(2n) = least composite number which is coprime to a(2n-1) and which is not already in the sequence.

%K easy,nonn

%O 1,1

%A _Amarnath Murthy_, Aug 17 2005

%E Better description from _Lior Manor_, Aug 23 2005

%E More terms from _R. J. Mathar_, Feb 08 2008