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 A071398 #21 Jun 06 2025 03:29:07
%S A071398 0,9,35,78,139,217,312,424,554,701,866,1048,1247,1464,1697,1949,2217,
%T A071398 2503,2806,3126,3464,3819,4192,4581,4988,5413,5854,6313,6790,7283,
%U A071398 7794,8323,8868,9431,10011,10609,11224,11856,12505,13172,13856,14558,15277
%N A071398 Rounded total surface area of a regular icosahedron with edge length n.
%D A071398 S. Selby, editor, CRC Basic Mathematical Tables, CRC Press, 1970, pp. 10-11.
%H A071398 Vincenzo Librandi, <a href="/A071398/b071398.txt">Table of n, a(n) for n = 0..10000</a>
%H A071398 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Icosahedron.html">Icosahedron</a>
%H A071398 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PlatonicSolid.html">Platonic Solid</a>
%F A071398 a(n) = round(5 * n^2 * sqrt(3)).
%e A071398 a(4)=139 because round(5*4^2*sqrt(3)) = round(80*1.73205...) = round(138.56...) = 139.
%t A071398 With[{c=5Sqrt[3]},Round[c Range[0,50]^2]] (* _Harvey P. Dale_, May 20 2011 *)
%o A071398 (PARI) for(n=0,100,print1(round(5*n^2*sqrt(3)),","))
%o A071398 (Magma) [Round(5 * n^2 * Sqrt(3)): n in [0..50]]; // _Vincenzo Librandi_, May 21 2011
%o A071398 (Python)
%o A071398 from math import isqrt
%o A071398 def A071398(n): return (m:=isqrt(k:=75*n**4))+int(k>m*(m+1)) # _Chai Wah Wu_, Jun 05 2025
%Y A071398 Cf. A070169 (tetrahedron), A033581 (cube), A071396 (octahedron), A071397 (dodecahedron), A071402 (volume of icosahedron).
%K A071398 easy,nonn
%O A071398 0,2
%A A071398 _Rick L. Shepherd_, May 29 2002