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 A380990 #11 Feb 12 2025 14:23:13
%S A380990 1,1,2,5,11,31,85,262,764,2255,6341,17221,43994,106205,239367,502611,
%T A380990 977791,1771624,2989373,4687803,6819069,9234529,11622453,13527854,
%U A380990 14571011,14643347,13747913,12041014,9905945,7763985,5805906,4139266,2858796,1971455,1368967,942226,618148,368480,186275,73649,20236,3476,400,96,27,12,2,1
%N A380990 Number of free polyominoes with n cells with at most 4 collinear cell centers on any line in the plane.
%H A380990 Dave Budd, <a href="https://github.com/daveisagit/collinear-polyominoes">python code</a>
%F A380990 a(n) = Sum_{k=1..4} A377942(n,k).
%o A380990 (Python) # See links
%Y A380990 Cf. A000105, A377942, A378169.
%K A380990 nonn,fini,full,nice
%O A380990 1,3
%A A380990 _Dave Budd_, Feb 11 2025