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a(1)=1 and, for n>1, a(n)=a(n-1)+Floor(3n/4) if n is even, else a(n)=smallest positive integer which has not yet appeared in the sequence.
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%I #2 Mar 30 2012 17:37:53

%S 1,3,2,5,4,8,6,12,7,15,9,18,10,20,11,23,13,27,14,29,16,32,17,35,19,39,

%T 21,42,22,44,24,48,25,51,26,53,28,56,30,60,31,63,33,66,34,68,36,72,37,

%U 75,38,77,40,80,41,83,43,87,45,90,46,92,47,95,49,99,50,101,52,104,54

%N a(1)=1 and, for n>1, a(n)=a(n-1)+Floor(3n/4) if n is even, else a(n)=smallest positive integer which has not yet appeared in the sequence.

%C Conjecture. For even n, the ratio a(n)/a(n-1) is asymptotic to 2 as n becomes large. (At n=3000, the ratio is 2.0004446.)

%Y Cf. A094077.

%K nonn

%O 1,2

%A _John W. Layman_, Jul 08 2004