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 A197723 #59 Feb 16 2025 08:33:15
%S A197723 4,7,1,2,3,8,8,9,8,0,3,8,4,6,8,9,8,5,7,6,9,3,9,6,5,0,7,4,9,1,9,2,5,4,
%T A197723 3,2,6,2,9,5,7,5,4,0,9,9,0,6,2,6,5,8,7,3,1,4,6,2,4,1,6,8,8,8,4,6,1,7,
%U A197723 2,4,6,0,9,4,2,9,3,1,3,4,9,7,9,4,2,0,5,2,2,3,8,0,1,3,1,7,5,6,0,1,9,7,3,2,2
%N A197723 Decimal expansion of (3/2)*Pi.
%C A197723 As radians, this is equal to 270 degrees or 300 gradians.
%C A197723 Multiplying a number by -i (with i being the imaginary unit sqrt(-1)) is equivalent to rotating it by this number of radians on the complex plane.
%C A197723 Named 'Pau' by Randall Munroe, as a humorous compromise between Pi and Tau. - _Orson R. L. Peters_, Jan 08 2017
%C A197723 (3*Pi/2)*a^2 is the area of the cardioid whose polar equation is r = a*(1+cos(t)) and whose Cartesian equation is (x^2+y^2-a*x)^2 = a^2*(x^2+y^2). The length of this cardioid is 8*a. See the curve at the Mathcurve link. - _Bernard Schott_, Jan 29 2020
%H A197723 Ivan Panchenko, <a href="/A197723/b197723.txt">Table of n, a(n) for n = 1..1000</a>
%H A197723 Robert Ferréol, <a href="https://www.mathcurve.com/courbes2d.gb/cardioid/cardioid.shtml">Cardioid</a>, Mathcurve.
%H A197723 Randall Munroe, <a href="http://xkcd.com/1292/">xkcd: Pi vs. Tau</a>
%H A197723 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Cardioid.html">Cardioid</a>
%H A197723 <a href="/index/Tra#transcendental">Index entries for transcendental numbers</a>
%F A197723 2*Pi - Pi/2 = Pi + Pi/2.
%F A197723 Equals Integral_{t=0..Pi} (1+cos(t))^2 dt. - _Bernard Schott_, Jan 29 2020
%F A197723 Equals -4 + Sum_{k>=1} (k+1)*2^k/binomial(2*k,k). - _Amiram Eldar_, Aug 19 2020
%e A197723 4.712388980384689857693965074919254326296...
%p A197723 Digits:=100: evalf(3*Pi/2); # _Wesley Ivan Hurt_, Jan 08 2017
%t A197723 RealDigits[3Pi/2, 10, 105][[1]]
%o A197723 (PARI) 3*Pi/2 \\ _Charles R Greathouse IV_, Jul 06 2018
%Y A197723 Cf. A019669, A003881, A347152.
%K A197723 nonn,cons
%O A197723 1,1
%A A197723 _Alonso del Arte_, Oct 17 2011