%I #12 Oct 26 2019 21:59:50
%S 1,1,2,3,4,4,4,5,6,6,6,6,6,6,6,7,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,9,10,
%T 10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,
%U 10,10,10,10,10,10,10,11,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12
%N a(0) = 1; a(n) = the number of earlier terms, a(k), where gcd(a(k), a(floor(k/2))) = 1.
%e Among terms a(0) through a(8) (1,1,2,3,4,4,4,5,6), a(0) is coprime to a(0), a(1) is coprime to a(0), a(2) is coprime to a(1), a(3) is coprime to a(1), a(6) is coprime to a(3) and a(7) is coprime to a(3). There are 6 such coprime pairs in the range, so a(9) = 6.
%t f[l_List] := Append[l, Count[Table[GCD[l[[k]], l[[Floor[(k + 1)/2]]]], {k, Length[l]}], 1]];Nest[f, {1}, 80] (* _Ray Chandler_, Oct 17 2006 *)
%K nonn
%O 0,3
%A _Leroy Quet_, Oct 10 2006
%E Extended by _Ray Chandler_, Oct 17 2006