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 A357284 #8 Nov 09 2022 07:56:32
%S A357284 0,0,0,0,1,4,13,34,83,188,413,878,1839,3792,7761,15762,31891,64276,
%T A357284 129301,259606,520727,1043480,2090009,4184090,8374299,16756764,
%U A357284 33525789,67067934,134160415,268353568,536756257,1073578018,2147254307,4294639652,8589475877
%N A357284 a(n) = (1/2)*A357283(n).
%H A357284 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (4,-3,-6,10,-4).
%F A357284 a(n) = 4*a(n-1) - 3*a(n-2) - 6*a(n-3) + 10*a(n-4) - 4*a(n-5).
%F A357284 G.f.: (x^4)/((-1 + x)^2 (1 - 2 x - 2 x^2 + 4 x^3)).
%F A357284 a(n) = Sum_{i=0..n-2} A274230(i). - _Ivan N. Ianakiev_, Nov 08 2022
%t A357284 s[n_] := s[n] = Select[Subsets[Range[n]], Length[#] >= 2 &]; (* note size >=2 *)
%t A357284 a[n_] := Select[s[n], #[[2]] + #[[1]] < #[[-1]] &]
%t A357284 (1/2)Table[Length[a[n]], {n, 0, 18}]
%Y A357284 Cf. A357283, A274230.
%K A357284 nonn,easy
%O A357284 0,6
%A A357284 _Clark Kimberling_, Sep 27 2022