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a(1)=1 and, for n>1, a(n)=a(n-1)+n if n is even and a(n)=smallest positive integer which has not yet appeared in the sequence if n is odd.
8

%I #8 Apr 20 2020 03:50:17

%S 1,3,2,6,4,10,5,13,7,17,8,20,9,23,11,27,12,30,14,34,15,37,16,40,18,44,

%T 19,47,21,51,22,54,24,58,25,61,26,64,28,68,29,71,31,75,32,78,33,81,35,

%U 85,36,88,38,92,39,95,41,99,42,102,43,105,45,109,46,112,48,116,49,119

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

%C A001951 and A001952 are the bisections of this sequence. - _Klaus Brockhaus_ and _Henry Bottomley_, Feb 04 2006. This implies the asymptotic result stated in the formula line.

%F For even n, the ratio a(n)/a(n-1) is asymptotic to 1+sqrt(2) as n becomes large.

%K nonn

%O 1,2

%A _John W. Layman_, Apr 29 2004