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%I A091780 #11 Nov 27 2017 00:22:37
%S A091780 3,6,9,12,15,10,5,20,25,30,21,14,7,28,35,40,45,18,27,24,33,22,11,44,
%T A091780 55,50,65,26,13,52,39,36,51,34,17,68,85,60,57,38,19,76,95,70,49,42,63,
%U A091780 48,69,46,23,92,115,80,75,54,81,66,77,56,91,78,87,58,29,116,145,90,93,62
%N A091780 Alternately odd and even numbers such that a(n) is the least number not included earlier and has a common factor with a(n-1).
%C A091780 The sequence contains all the numbers except powers of 2.
%p A091780 A091780 := proc(nmax) local a,nstrt; a := [3] ; while nops(a) < nmax do if nops(a) mod 2 = 0 then nstrt := 5; else nstrt := 4 ; fi ; while nstrt in a or gcd(nstrt,op(-1,a)) < 2 do nstrt := nstrt+2 ; od ; a := [op(a),nstrt] ; od ; a ; end: A091780(80) ; # _R. J. Mathar_, Jul 26 2007
%K A091780 nonn
%O A091780 1,1
%A A091780 _Amarnath Murthy_, Feb 16 2004
%E A091780 More terms from _R. J. Mathar_, Jul 26 2007

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