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 A277921 #7 Nov 12 2016 17:53:22
%S A277921 0,1,4,23,142,950,6662,48420,361378,2753687,21334313,167551836,
%T A277921 1330894754,10673486660,86306300366,702872359332,5759986152740,
%U A277921 47463395965108,393027545388119,3268814565684836,27294209365111429,228718165320327356,1922825557218427271
%N A277921 Number of positive walks with n steps {-4,-3,-2,-1,0,1,2,3,4} starting at the origin, ending at altitude 2, and staying strictly above the x-axis.
%H A277921 Alois P. Heinz, <a href="/A277921/b277921.txt">Table of n, a(n) for n = 0..1053</a>
%H A277921 C. Banderier, C. Krattenthaler, A. Krinik, D. Kruchinin, V. Kruchinin, D. Nguyen, and M. Wallner, <a href="https://arxiv.org/abs/1609.06473">Explicit formulas for enumeration of lattice paths: basketball and the kernel method</a>, arXiv:1609.06473 [math.CO], 2016.
%Y A277921 Cf. A276904, A276852, A276901, A276902, A276903.
%K A277921 nonn,walk
%O A277921 0,3
%A A277921 _David Nguyen_, Nov 04 2016