Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #14 Aug 26 2019 14:24:05
%S 1,4,4,16,256,65536,4294967296,18446744073709551616,
%T 340282366920938463463374607431768211456,
%U 115792089237316195423570985008687907853269984665640564039457584007913129639936
%N a(1) = 1, a(2) = 4, a(n) = product of the previous terms for n >= 3.
%H Vincenzo Librandi, <a href="/A165422/b165422.txt">Table of n, a(n) for n = 1..13</a>
%F a(1) = 1, a(2) = 4, a(n) = Product_{i=1..n-1} a(i), n >= 3.
%F a(1) = 1, a(2) = 4, a(n) = A000302(2^(n-3)) = A001146(n-2) = 2^(2^(n-2)), n >= 3.
%F a(1) = 1, a(2) = 4, a(3) = 4, a(n) = (a(n-1))^2, n >= 4.
%t a[1]:= 1; a[2]:= 4; a[n_] := Product[a[j], {j,1,n-1}]; Table[a[n], {n,1,12}] (* _G. C. Greubel_, Oct 19 2018 *)
%t Join[{1,4},NestList[#^2&,4,10]] (* _Harvey P. Dale_, Aug 26 2019 *)
%o (PARI) {a(n) = if(n==1, 1, if(n==2, 4, prod(j=1,n-1, a(j))))};
%o for(n=1,10, print1(a(n), ", ")) \\ _G. C. Greubel_, Oct 19 2018
%K nonn
%O 1,2
%A _Jaroslav Krizek_, Sep 17 2009