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%I #43 Jan 11 2020 15:57:46
%S 0,1,4,16,27,256,3125,46656,65536,823543,16777216,387420489,
%T 10000000000,285311670611,7625597484987,8916100448256,302875106592253,
%U 11112006825558016,437893890380859375,18446744073709551616,827240261886336764177,39346408075296537575424,1978419655660313589123979,104857600000000000000000000
%N Perfect hyper-4 powers: a^^b, where b <> 1.
%C a^^b is the right associative power tower a^a^...^a^a of height b. a^^-1= 0 and a^^0 = 1. We exclude b=1 because otherwise all natural numbers would be in the sequence.
%e Numbers written as power towers include:
%e 5^^2 = 5^5 = 3125;
%e 3^^3 = 3^3^3 = 3^27 = 7625597484987;
%e 2^^4 = 2^2^2^2 = 2^2^4 = 2^16 = 65536;
%e 0^^5 = 0^0^0^0^0 = 0^0^0^1 = 0^0^0 = 0^1 = 0;
%Y Cf. A004231, A002488.
%K nonn
%O 1,3
%A _Natan Arie Consigli_, May 07 2015
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