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 A011545 #72 Mar 15 2024 23:39:50
%S A011545 3,31,314,3141,31415,314159,3141592,31415926,314159265,3141592653,
%T A011545 31415926535,314159265358,3141592653589,31415926535897,
%U A011545 314159265358979,3141592653589793,31415926535897932,314159265358979323,3141592653589793238,31415926535897932384
%N A011545 a(n) is the integer whose decimal digits are the first n+1 decimal digits of Pi.
%C A011545 Number of collisions occurring in a system consisting of an infinitely massive, rigid wall at the origin, a ball with mass m stationary at position x1 > 0, and a ball with mass (10^2n)m at position x2 > x1 and rolling toward the origin, assuming perfectly elastic collisions and no friction. - _Richard Holmes_, Jun 17 2021
%C A011545 Wolfgang Haken (1977) conjectured that no term of this sequence is a perfect square, and estimated the probability that this conjecture is false to be smaller than 10^-9. - _Paolo Xausa_, Jul 15 2023
%D A011545 Martin Gardner, Fractal Music, Hypercards and More: Mathematical Recreations from Scientific American Magazine, W. H. Freemand and Company, New York, NY, 1992, pp. 274-275.
%H A011545 Paolo Xausa, <a href="/A011545/b011545.txt">Table of n, a(n) for n = 0..100</a>
%H A011545 G. Galperin, <a href="https://www.maths.tcd.ie/~lebed/Galperin.%20Playing%20pool%20with%20pi.pdf">Playing pool with π (the number π from a billiard point of view)</a>, Regular and Chaotic Dynamics, 8 (2003), 375-394.
%H A011545 Wolfgang Haken, <a href="https://doi.org/10.1002/jgt.3190010304">An attempt to understand the four color problem</a>, in Journal of Graph Theory, Vol. 1, Issue 3, 1977, pp. 193-206.
%H A011545 G. Sanderson, <a href="https://youtu.be/jsYwFizhncE">Why do colliding blocks compute pi?</a>, a 3Blue1Brown YouTube video, Jan 20 2019.
%F A011545 a(n) = floor(Pi*10^n).
%t A011545 s=RealDigits[Pi, 10, 30][[1]]; Table[FromDigits[Take[s, n]], {n, Length[s]}]
%t A011545 (* Or: *)
%t A011545 a[n_] := IntegerPart[Pi*10^n]; Table[a[n], {n, 0, 9}] (* _Peter Luschny_, Mar 15 2024 *)
%o A011545 (PARI) A011545(n)={localprec(n+3); Pi\10^-n} \\ _M. F. Hasler_, Mar 15 2024
%Y A011545 Cf. A000796 (decimal expansion of Pi), A089281, A078604, A089282, A089283, A089284, A089285, A089286, A089287, A089288, A089289, A046974, A089290.
%K A011545 nonn,base
%O A011545 0,1
%A A011545 _N. J. A. Sloane_
%E A011545 Definition corrected by _M. F. Hasler_, Mar 15 2024