%I #6 Jan 11 2020 15:57:47
%S 1,2,4,9,64
%N a(n) = H_{n-1}(n,n).
%C H is the hyperoperation function see A054871 for more information.
%C This sequence is a shifted version of the weak Ackermann numbers H_n(n,n).
%Y Cf. A189896 (H_n(n,n)), A054871.
%K nonn,bref
%O 0,2
%A _Natan Arie Consigli_, Apr 09 2016