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 A303617 #19 Apr 27 2018 17:08:35
%S A303617 8,8,3,9,4,3,9,2,4,0,9,1,9,0,4,9,0,9,4,5,6,6,9,8,0,2,4,4,3,6,2,0,3,5,
%T A303617 7,4,1,7,1,0,0,2,8,4,6,3,7,8,3,0,9,2,7,9,6,0,4,1,8,6,3,3,9,4,0,1,1,3,
%U A303617 8,1,0,7,1,4,5,3,7,8,6,1,4,5,5,8,0,9,4,2,0,9,6,7,3
%N A303617 Decimal expansion of Sum_{k >= 0} 2^(2*k+1)/Product_{i = 0..k} (2*i+1).
%F A303617 Equals e^2*sqrt(Pi/2)*erf(sqrt(2)) = A072334*A069998*A110894.
%e A303617 8.83943924091904909456698024436203574171002846378309279604186339401138107...
%e A303617 2/1 + 2^3/(1*3) + 2^5/(1*3*5) + 2^7/(1*3*5*7) + 2^9/(1*3*5*7*9) + 2^11/(1*3*5*7*9*11) + 2^13/(1*3*5*7*9*11*13) + ...
%t A303617 RealDigits[E^2 Sqrt[Pi/2] Erf[Sqrt[2]], 10, 100][[1]]
%o A303617 (PARI) suminf(k=0, 2^(2*k+1)/prod(i=0, k, (2*i+1))) \\ _Michel Marcus_, Apr 27 2018
%Y A303617 Cf. A001147, A004171.
%Y A303617 Cf. A069998, A072334, A110894.
%K A303617 nonn,cons
%O A303617 1,1
%A A303617 _Bruno Berselli_, Apr 27 2018