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A165421 a(1) = 1, a(2) = 3, a(n) = product of the previous terms for n >= 3.

%I A165421 #19 Jan 31 2022 14:43:30
%S A165421 1,3,3,9,81,6561,43046721,1853020188851841,
%T A165421 3433683820292512484657849089281,
%U A165421 11790184577738583171520872861412518665678211592275841109096961
%N A165421 a(1) = 1, a(2) = 3, a(n) = product of the previous terms for n >= 3.
%C A165421 Essentially a duplicate of A011764. - _N. J. A. Sloane_, Oct 06 2009
%H A165421 Vincenzo Librandi, <a href="/A165421/b165421.txt">Table of n, a(n) for n = 1..14</a>
%F A165421 a(1) = 1, a(2) = 3, a(n) = Product_{i=1..n-1} a(i), n >= 3.
%F A165421 a(1) = 1, a(2) = 3, a(n) = A000244(2^(n-3)) = A011764(n-3) = 3^(2^(n-3)), n >= 3.
%F A165421 a(1) = 1, a(2) = 3, a(3) = 3, a(n) = (a(n-1))^2, n >= 4.
%t A165421 a[1]:= 1; a[2]:= 3; a[n_]:= Product[a[j], {j,1,n-1}]; Table[a[n], {n, 1, 12}] (* _G. C. Greubel_, Oct 19 2018 *)
%t A165421 nxt[{prd_,a_}]:=Module[{c=prd*a},{c,prd*a}]; Join[{1,3},Rest[ NestList[ nxt,{1,3},10][[All,1]]]] (* _Harvey P. Dale_, Jan 31 2022 *)
%o A165421 (PARI) {a(n) = if(n==1, 1, if(n==2, 3, prod(j=1,n-1, a(j))))};
%o A165421 for(n=1,10, print1(a(n), ", ")) \\ _G. C. Greubel_, Oct 19 2018
%K A165421 nonn
%O A165421 1,2
%A A165421 _Jaroslav Krizek_, Sep 17 2009