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 A349009 #11 Dec 19 2024 11:46:19
%S A349009 9,7,6,1,6,4,0,0,2,9,1,2,7,0,3,5,1,3,4,0,6,4,0,7,1,5,8,0,8,4,2,1,1,1,
%T A349009 2,9,7,2,6,3,1,2,1,9,9,3,1,7,3,2,6,9,0,5,2,4,3,4,9,4,8,8,0,3,0,0,8,2,
%U A349009 8,7,3,8,6,7,9,6,5,1,1,6,0,1,1,0,7,5,0,4,2,4,7,8,8,5,1,6,1,5,8,6,3,8,6,6,9
%N A349009 Decimal expansion of the area of the convex hull around the R5 dragon fractal.
%C A349009 The fractal is taken scaled to unit length from curve start to end.
%C A349009 In the sum formula below, all HAtermf(j) > 0 and a simple upper bound is Sum_{j>=k} HAtermf(j) < 1/sqrt(5)^k.
%H A349009 Kevin Ryde, <a href="/A349009/b349009.txt">Table of n, a(n) for n = 0..10000</a>
%H A349009 Kevin Ryde, <a href="http://user42.tuxfamily.org/r5dragon/index.html">Iterations of the R5 Dragon Curve</a>, see index "HAf".
%H A349009 Kevin Ryde, <a href="/A349009/a349009.gp.txt">PARI/GP Code</a>
%F A349009 Equals 17/25 + Sum_{j>=1} HAtermf(j), where complex b=1+2*i and:
%F A349009 HAtermf(j) = (1/25)*(6*HAgrowf(1/b^j) + 2*HAgrowf((4+i)/b^j)),
%F A349009 HAgrowf(z) = MinReIm(ShearIm(RotQ(z))),
%F A349009 MinReIm(z) = min(abs(Re z), abs(Im z)),
%F A349009 ShearIm(z) = z + i*Im(z),
%F A349009 RotQ(z) = z if sign(Re z) = sign(Im z), or RotQ(z) = z*i otherwise.
%F A349009 Equals lim_{n->oo} A349008(n)/5^n.
%e A349009 0.97616400291270351340640715808421112...
%o A349009 (PARI) \\ See links.
%Y A349009 Cf. A349008 (finite areas), A349010 (fractal perimeter).
%K A349009 cons,nonn
%O A349009 0,1
%A A349009 _Kevin Ryde_, Nov 06 2021