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 A175129 #11 Jun 20 2021 13:19:40 %S A175129 1,3,9,27,729,531441,282429536481,79766443076872509863361, %T A175129 6362685441135942358474828762538534230890216321 %N A175129 a(0)=1, a(1)=3; for n>=2, a(n) = 3^A042950(n-2). %Y A175129 Cf. A042950, A167182, A172489, A173260. %K A175129 nonn %O A175129 0,2 %A A175129 _Giovanni Teofilatto_, Feb 17 2010 %E A175129 Revised by _N. J. A. Sloane_, Jun 20 2021