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 A140319 #22 Jul 09 2025 10:17:29
%S A140319 1,2,9,1953125
%N A140319 Exponential primorial: a(n)=prime(n)^a(n-1), a(0)=1, where prime(n)=A000040(n).
%C A140319 The next term is too large to include.
%H A140319 Jonathan Sondow, <a href="https://mathworld.wolfram.com/ExponentialFactorial.html">Exponential Factorial</a>, Eric Weisstein's World of Mathematics.
%F A140319 Sum_{n>=0} 1/a(n) = A167155. - _Amiram Eldar_, Nov 15 2020
%e A140319 a(1) = prime(1)^a(0) = 2^1 = 2.
%e A140319 a(2) = 3^2 = 9.
%e A140319 a(3) = 5^9 = 1953125.
%e A140319 a(4) = 7^1953125 has 1650583 digits, starting with 12864794... and ending in ...31920807. - _M. F. Hasler_, Nov 03 2009
%p A140319 P:=proc(n) local a,i; a:=2; print(a); for i from 2 by 1 to n do a:=ithprime(i)^a; print(a); od; end: P(5);
%t A140319 a[0]=1;a[n_]:=Prime[n]^a[n-1];Array[a,4,0] (* _James C. McMahon_, Jul 08 2025 *)
%o A140319 (PARI) A140319(n)=if(n,prime(n)^A140319(n-1),1) \\ _M. F. Hasler_, Nov 03 2009
%Y A140319 Cf. A002110, A049384, A139802, A167155.
%Y A140319 Cf. A152859 (alternate definition: start with a(0)=0), A167155.
%K A140319 easy,nonn
%O A140319 0,2
%A A140319 _Paolo P. Lava_ and _Giorgio Balzarotti_, May 26 2008
%E A140319 Corrected offset/definition, and initial a(0)=1 from _M. F. Hasler_, Nov 03 2009