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 A215578 #10 Nov 11 2017 20:45:18
%S A215578 1,0,6,2,5,0,0,0,0,0,0,0,0,1,3,1,1,3,7,2,6,5,2,3,9,7,0,9,2,5,0,7,2,3,
%T A215578 4,6,8,5,5,1,9,5,4,3,1,3,5,3,0,2,4,9,9,3,8,9,7,5,8,8,2,5,2,3,8,0,8,1,
%U A215578 2,4,4,5,5,8,1,2,3,3,1,0,9,3,4,1,4,0,6,0,5,6,4,4,9,0,2,3,0,6,0,2,2,1,7,3,1
%N A215578 Decimal expansion of Sum_{n>=1} 1/n^(n^n).
%C A215578 A more general function is L(z) = sum(n=1,Infinity,1/n^^z).
%C A215578 What is the value of L(4)?
%C A215578 L(4) = 1.0000152587890625000... where the next 3 trillion decimal places are 0. - _Charles R Greathouse IV_, Sep 20 2012
%H A215578 Wikipedia, <a href="http://en.wikipedia.org/wiki/Tetration">Tetration</a>
%e A215578 1.062500000000131137265239709250723468551954313530249 . . .
%o A215578 (PARI) suminf(n=1,1/n^(n^n))
%Y A215578 Cf. A073009, A002488.
%K A215578 cons,nonn
%O A215578 1,3
%A A215578 _Balarka Sen_, Aug 16 2012