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 A124507 #40 Sep 08 2022 08:45:28
%S A124507 1,4,23,111,535,2575,12391,59609,286751,1379410,6635623,31920519,
%T A124507 153552935,738662922,3553321280,17093171648,82226315585,395547831244,
%U A124507 1902773895292,9153250784394,44031505860632,211812562992413,1018919543279304,4901489415968642
%N A124507 a(n) = floor(exp(n*Pi/2)).
%D A124507 Roger Penrose, The Road to Reality, (2005), p. 88 (figure 5.3).
%H A124507 G. C. Greubel, <a href="/A124507/b124507.txt">Table of n, a(n) for n = 0..1000</a>
%p A124507 Digits:= 2000:
%p A124507 a:= n-> floor(exp(n*Pi/2)):
%p A124507 seq(a(n), n=0..30); # _Alois P. Heinz_, Nov 25 2018
%t A124507 Table[ Floor@ Exp[n*Pi/2], {n, 0, 21}] (* _Robert G. Wilson v_, Dec 31 2006 *)
%o A124507 (PARI) vector(30, n, n--; floor(exp(n*Pi/2))) \\ _G. C. Greubel_, Nov 25 2018
%o A124507 (Magma) R:= RealField(10); [Floor(Exp(n*Pi(R)/2)): n in [0..30]]; // _G. C. Greubel_, Nov 25 2018
%o A124507 (Sage) [floor(exp(n*pi/2)) for n in range(30)] # _G. C. Greubel_, Nov 25 2018
%Y A124507 Cf. A062360 (even bisection), A042972.
%K A124507 nonn
%O A124507 0,2
%A A124507 _Zacariaz Martinez_, Dec 27 2006
%E A124507 Edited and extended by _Robert G. Wilson v_, Dec 31 2006
%E A124507 Comments edited by _Jon E. Schoenfield_, Nov 25 2018