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 A071400 #9 Feb 16 2025 08:32:46
%S A071400 0,0,4,13,30,59,102,162,241,344,471,627,815,1036,1294,1591,1931,2316,
%T A071400 2749,3233,3771,4366,5020,5736,6517,7366,8285,9279,10348,11497,12728,
%U A071400 14044,15447,16941,18528,20211,21994,23878,25867,27963,30170,32490
%N A071400 Rounded volume of a regular octahedron with edge length n.
%D A071400 S. Selby, editor, CRC Basic Mathematical Tables, CRC Press, 1970, pp. 10-11.
%H A071400 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Octahedron.html">Octahedron</a>
%F A071400 a(n) = round(n^3 * sqrt(2)/3)
%e A071400 a(4)=30 because round(4^3*sqrt(2)/3)=round(64*.47140...)=round(30.169...)=30.
%t A071400 With[{c=Sqrt[2]/3},Table[Round[n^3*c],{n,0,50}]] (* _Harvey P. Dale_, May 20 2014 *)
%o A071400 (PARI) for(n=0,100,print1(round(n^3*sqrt(2)/3),","))
%Y A071400 Cf. A000578 (cube), A071399 (tetrahedron), A071401 (dodecahedron), A071402 (icosahedron), A071396 (total surface area of octahedron).
%K A071400 easy,nonn
%O A071400 0,3
%A A071400 _Rick L. Shepherd_, May 29 2002