This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A139802 #8 Feb 14 2024 19:49:51 %S A139802 1,2,3,16,125,2821109907456, %T A139802 4337654948097993282537354757263188251697832994620405101744893017744569432720994168089672192211758909320807 %N A139802 a(1)=1, a(2)=2, a(n)=n^a(n-2). %C A139802 Exponential double factorial. %C A139802 The next term is too large to include. %e A139802 a(1)=1; %e A139802 a(2)=2; %e A139802 a(3)=3^1=3; %e A139802 a(4)=4^2=16; %e A139802 a(5)=5^3=125; %e A139802 a(6)=6^16=2821109907456; %e A139802 etc. %t A139802 a[1]=1; a[2]=2; a[n_]:=n^a[n-2]; Array[a,7] (* _Stefano Spezia_, Feb 14 2024 *) %Y A139802 Cf. A049384. %K A139802 easy,nonn %O A139802 1,2 %A A139802 _Paolo P. Lava_ and _Giorgio Balzarotti_, May 22 2008