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 A173171 #16 Sep 30 2018 22:39:48
%S A173171 -1,0,49,23762,25421763,48225038404,142786923879605,
%T A173171 608447515452613206,3527836867501829594887,26710782540478226038759688,
%U A173171 255922222218837615280903143609,3026917140685147530327256796600410
%N A173171 a(n) = - sin^2((2n-1)*arccos(sqrt n)) = sin^2((2n-1)*arcsin(sqrt n)) - 1.
%H A173171 Vincenzo Librandi, <a href="/A173171/b173171.txt">Table of n, a(n) for n = 0..170</a>
%t A173171 Table[Round[-N[ Sin[(2 n - 1) ArcCos[Sqrt[n]]]^2, 100]], {n, 0, 20}] (* _Artur Jasinski_, Feb 11 2010; Typo fixed by _Vincenzo Librandi_, Jun 29 2014 *)
%Y A173171 Cf. A132592, A146311, A146312, A146313, A173115, A173116 A173121, A173127, A173128, A173129, A173130, A173131, A173133, A173134, A173148, A173151, A173170.
%K A173171 sign
%O A173171 0,3
%A A173171 _Artur Jasinski_, Feb 11 2010