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 A306980 #8 Mar 20 2019 04:36:30
%S A306980 1,1,5,9,1,7,3,3,1,9,6,3,2,1,7,4,6,9,5,0,7,8,5,6,6,6,2,4,0,6,7,4,3,7,
%T A306980 8,7,6,8,4,4,6,3,5,5,1,1,9,5,5,9,3,9,5,5,3,9,0,2,4,4,9,7,4,6,9,9,6,9,
%U A306980 5,3,5,6,5,1,4,1,1,6,8,4,3,4,5,0,0,4,2
%N A306980 Decimal expansion of the sum of the reciprocals of the star numbers (A003154).
%F A306980 Equals Sum_{n>=1} 1/(6*n*(n-1) + 1) = x * tan(x) with x = Pi/(2*sqrt(3)).
%e A306980 1.15917331963217469507856662406743787684463551195593...
%t A306980 s[n_]:=6*n*(n-1) + 1; RealDigits[Sum[1/s[n], {n,1,Infinity}], 10, 100][[1]]
%Y A306980 Cf. A003154, A093766 (Pi/(2*sqrt(3))).
%K A306980 nonn,cons
%O A306980 1,3
%A A306980 _Amiram Eldar_, Mar 18 2019