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%I #7 Dec 08 2017 17:11:35
%S 1,1,3,9,171,332572817028187686275682948600327513806149983112761
%N a(1)=1, a(2)=1, a(n)=(2^a(n-1) + 1)/a(n-2).
%C Are all terms integers?
%t nxt[{a_,b_}]:={b,(2^b+1)/a}; NestList[nxt,{1,1},5][[All,1]]//Quiet (* _Harvey P. Dale_, Dec 08 2017 *)
%K nonn
%O 1,3
%A _Benoit Cloitre_, Dec 06 2002