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 A213681 #22 Apr 21 2018 11:23:07
%S A213681 6,14,94,4414,9741694,47450300994814,1125765532249223239027447294,
%T A213681 633674016800188444301553476967536472012841942973961214
%N A213681 a(n) = a(n-1)^2/2 - 4 with a(0) = 6.
%C A213681 The next term has 108 digits. - _Harvey P. Dale_, Apr 21 2018
%F A213681 a(n) = 4*cosh(2^n*arccosh(3/2)).
%F A213681 a(n) = 2*A005248(2^n). [_Bruno Berselli_, Mar 04 2013]
%e A213681 a(2) = a(1)^2/2-4 = 14^2/2-4 = 94.
%t A213681 NestList[#^2/2-4&,6,8] (* _Harvey P. Dale_, Apr 21 2018 *)
%o A213681 (Sage)
%o A213681 var('x')
%o A213681 p=x^2/2-4
%o A213681 s=[6]
%o A213681 for i in [0..8]:
%o A213681 s=s+[p(s[i])]
%o A213681 show(s)
%Y A213681 Cf. A005248.
%K A213681 nonn
%O A213681 0,1
%A A213681 _Jose Eduardo Blazek_, Mar 04 2013