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 A340315 #13 Jan 07 2021 21:31:35
%S A340315 3,7,8,3,4,4,0,9,8,3,5,0,0,7,9,7,6,6,6,6,8,3,6,8,1,6,3,9,2,2,7,9,8,9,
%T A340315 1,5,6,1,0,7,5,0,8,5,8,9,8,6,0,1,1,2,7,4,3,1,9,8,1,9,8,0,6,3,6,6,9,1,
%U A340315 0,7,1,0,1,1,2,5,2,3,2,2,7,6,3,6,3,4,2,2,0,6,6,9,8,1,1,9,3,7,1,8,5,6,3,9
%N A340315 Decimal expansion of sum of reciprocals of A000111(n) (where A000111(n) is the n-th Euler or up/down number).
%C A340315 The series 1/1 + 1/1 + 1/1 + 1/2 + 1/5 + 1/16 + 1/61 + 1/272 + 1/1385 + 1/7936 + ... converges to 3.783440983500797666683...
%F A340315 Equals Sum_{k>=0} 1/A000111(k).
%e A340315 3.783440983500797666683...
%o A340315 (PARI) f(n)=if(n, 2*abs(polylog(-n, I)), 1); \\ A000111
%o A340315 suminf(n=0, 1/f(n)) \\ _Michel Marcus_, Jan 04 2021
%Y A340315 Cf. A000111, A001250, A173253.
%K A340315 nonn,cons
%O A340315 1,1
%A A340315 _Marco Ripà_, Jan 04 2021
%E A340315 More digits from _Alois P. Heinz_, Jan 06 2021