%I #7 Nov 07 2013 11:57:46
%S 0,1,2,2,4,4,4,4,16,16,16,16,16,16,16,16,65536,65536,65536,65536,
%T 65536,65536,65536,65536,65536,65536,65536,65536,65536,65536,65536,
%U 65536
%N a(1)=0; thereafter a(n) = 2^a(ceiling(n/2)).
%C a(33) through a(64) are 2^65536.
%F For n>2, a(n) = a tower of 2's of height ceiling(log_2(n))-1. E.g. a(17) = 2^2^2^2.
%Y Cf. A230863, A230874.
%K nonn
%O 1,3
%A _N. J. A. Sloane_, Nov 07 2013