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%I #15 Jul 23 2024 08:39:49
%S 0,1,4,256,
%T 13407807929942597099574024998205846127479365820592393377723561443721764030073546976801874298166903427690031858186486050853753882811946569946433649006084096
%N a(0) = 0; thereafter a(n+1) = 4^a(n).
%C Or, define two sequences by q(0) = 0, p(n) = 2^q(n), q(n+1) = p(n)^2; sequence gives q(n).
%C 4-ish analog of A014221 and A014222. - _Henry Bottomley_, Feb 16 2006
%t NestList[4^# &, 0, 4] (* _Paolo Xausa_, Jul 23 2024 *)
%Y Cf. A114560, A081651, A014221, A014222.
%K nonn
%O 0,3
%A _Jeremy Gardiner_, Feb 15 2006