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 A256131 #44 Jan 11 2020 15:57:46
%S A256131 3,12,20,100,10000000000
%N A256131 a(n) = H_n(10,2) where H_n is the n-th hyperoperator.
%C A256131 See A054871 for definitions and key links.
%C A256131 Sequence can be also be seen as a(0) = 3, a(1) = 12, a(n) = H_{n-1}(10,10) for n>1. - _Natan Arie Consigli_, Apr 22 2015; edited by _Danny Rorabaugh_, Oct 20 2015
%H A256131 Wikipedia, <a href="http://en.wikipedia.org/wiki/Hyperoperation">Hyperoperation</a>
%e A256131 a(0) = H_0(10,2) = 2+1 = 3;
%e A256131 a(1) = H_1(10,2) = 10+2 = 12;
%e A256131 a(2) = H_2(10,2) = 10*2 = 10+10 = 20;
%e A256131 a(3) = H_3(10,2) = 10^2 = 10*10 = 100;
%e A256131 a(4) = H_4(10,2) = 10^^2 = 10^10 = 10000000000;
%e A256131 a(5) = H_5(10,2) = 10^^^2 = 10^^10 = 10^10^10^10^10^10^10^10^10^10 = ... .
%Y A256131 Cf. A054871.
%K A256131 nonn
%O A256131 0,1
%A A256131 _Natan Arie Consigli_, Mar 15 2015
%E A256131 First terms corrected and hyperoperator notation implemented by _Danny Rorabaugh_, Oct 20 2015