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 A340841 #19 Feb 13 2021 15:05:36
%S A340841 1,5,1,0,6,3,7,4,4,8,1,3,0,9,5,4,8,5,2,8,4,6,1,9,7,4,9,6,0,8,0,2,4,5,
%T A340841 6,9,4,0,3,2,0,9,4,0,5,2,9,8,6,9,2,4,1,1,8,6,9,7,0,7,5,6,4,8,2,3,4,2,
%U A340841 2,6,6,3,3,2,2,3,7,5,9,7,6,7,6,5,1,9,8,4
%N A340841 Decimal expansion of Sum_{n>=0} 1/(n*2^n + 1).
%C A340841 This constant is the sum of reciprocals of Cullen numbers.
%F A340841 Equals Sum_{n>=0} 1/A002064(n).
%e A340841 1.5106374481309548528461974960802456940320940529869241186970756482342266...
%t A340841 First[RealDigits[NSum[1/(n*2^n+1), {n, 0, Infinity}, NSumTerms -> 100, Method -> {"NIntegrate", "MaxRecursion" -> 10}, WorkingPrecision -> 100]]] (* _Stefano Spezia_, Jan 24 2021 *)
%o A340841 (PARI) suminf(n=0, 1/(n*2^n + 1)) \\ _Michel Marcus_, Jan 24 2021
%Y A340841 Cf. A002064.
%K A340841 nonn,cons
%O A340841 1,2
%A A340841 _Marco Ripà_, Jan 23 2021