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 A134880 #13 Jan 15 2021 15:48:52
%S A134880 2,5,3,9,0,6,3,0,9,6,0,4,6,4,4,7,7,5,4,4,4,8,3,5,1,0,8,6,2,4,2,7,5,2,
%T A134880 2,1,7,0,0,3,7,2,6,4,0,0,4,4,1,8,1,3,1,3,3,3,7,0,7,2,6,6,4,5,8,5,4,1,
%U A134880 1,9,7,7,3,3,5,5,9,0,7,7,9,3,6,0,9,7,6,6,9,0,4,0,1
%N A134880 Decimal expansion of Sum_{k>=1} 1/(2^k)^(2^k).
%e A134880 0.25390630960464477544483510862427522170037264004418131333707266458541197733559...
%t A134880 RealDigits[N[Sum[1/(2^n)^(2^n), {n, 1, 30}], 200]][[1]]
%o A134880 (PARI) suminf(k=1, 1/(2^k)^(2^k)) \\ _Michel Marcus_, Jan 15 2021
%Y A134880 Cf. A073009, A100085, A134877, A134878, A134879.
%K A134880 nonn,cons
%O A134880 0,1
%A A134880 _Artur Jasinski_, Nov 14 2007