%I #7 Mar 30 2012 18:51:19
%S 2,4,5,16,64,7,4096,9,65536,11,1048576,13,16777216,15,268435456,256,
%T 18,17179869184,20,274877906944,22,4398046511104,24,70368744177664,26,
%U 1125899906842624,28,18014398509481984,30,288230376151711744,32
%N Earliest sequence where a(a(n))=4^n.
%H <a href="/index/Aa#aan">Index entries for sequences of the a(a(n)) = 2n family</a>
%e a(7)=a(a(6))=4^6=4096
%Y Cf. A038755, A038756.
%K nonn
%O 1,1
%A _Henry Bottomley_, May 03 2000