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 A204687 #43 Sep 18 2022 20:20:15 %S A204687 1,3,33,4323,74748993,22349647743307203, %T A204687 1998027016999666984531472383425633, %U A204687 15968447842642350164774423714587589071259011612916483703599782377123 %N A204687 a(n) = A204321(n)/4. %C A204687 Terms of the sequence can be presented as products of the following distinct prime factors: 1, 3, 3*11, 3*11*131, 3*11*131*17291, 3*11*131*17291*298995971. _Alexander R. Povolotsky_, Jan 19 2012 %C A204687 Those factors are A121897(m) for m >= 5. - _Alexander R. Povolotsky_, Jun 17 2012 %F A204687 a(n) = product(A126604(k), k=2...n) for n >= 2. %Y A204687 Cf. A204321, A126604, A121897. %K A204687 nonn %O A204687 1,2 %A A204687 _Alexander R. Povolotsky_, Jan 19 2012