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 A347303 #6 Aug 28 2021 11:38:00
%S A347303 0,1,3,15,21,183,309,1347,4041,17163,31329,149427,171081,1233963,
%T A347303 4422609,13628187,30794481,116887923,154627929,929468907,3253991841,
%U A347303 10227560643,26026830729,88788949947,255658392081,820517465043,2461552395129,7545284051787,20547702892161
%N A347303 a(n) = 3^(n-1) - lcm{1..n}.
%Y A347303 Cf. A003418, A347302.
%K A347303 nonn
%O A347303 1,3
%A A347303 _N. J. A. Sloane_, Aug 28 2021