%I #10 Jun 10 2024 00:04:52
%S 6,1,5,6,3,6,2,5,7,9,8,6,2,0,3,7,1,9,4,7,9,3,7,9,3,0,6,4,2,8,0,6,7,2,
%T 4,5,3,7,3,5,5,0,0,6,1,5,2,5,4,8,9,1,3,1,2,3,7,0,8,7,2,9,5,8,3,2,4,8,
%U 6,5,7,4,6,6,3,7,3,9,6,7,9,2,1,5,5,4,2,3,2,8,2,0,9,3,4,5,9,8,5,5
%N Length of the perimeter of the regular 9-gon with unit circumradius.
%H Paolo Xausa, <a href="/A365165/b365165.txt">Table of n, a(n) for n = 1..10000</a>
%F Equals 9*A272488.
%e 6.1563625798620371947937930642806724537...
%t First[RealDigits[18*Sin[Pi/9], 10, 100]] (* _Paolo Xausa_, Mar 19 2024 *)
%Y Cf. A019845 (5-gon), A010487 (4-gon), A365163 (7-gon), A365164 (8-gon), A272488 (edge length).
%K nonn,cons
%O 1,1
%A _R. J. Mathar_, Aug 24 2023