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 A272687 #9 Jun 08 2024 16:22:29
%S A272687 1,1,4,14,50,184,694,2670,10440,41374,165830,671084,2738334,11254362,
%T A272687 46547340,193592830,809165002,3397135168,14319385126,60576862358,
%U A272687 257109077584,1094541239294,4672423779086,19996407893908,85778157486910,368757697819570,1588465839532628,6855304750273902
%N A272687 First differences of A078482.
%t A272687 Differences[CoefficientList[Series[(1-3 x+x^2-Sqrt[1-6 x+7 x^2-2 x^3+x^4])/(2 x),{x,0,40}],x]] (* _Harvey P. Dale_, Jun 08 2024 *)
%Y A272687 Cf. A078482, A272686 (second differences).
%K A272687 nonn
%O A272687 0,3
%A A272687 _N. J. A. Sloane_, May 24 2016