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 A143849 #14 Jul 11 2024 21:43:40 %S A143849 0,1,3,1,-17,-2719,-33231617,-1990664248298239, %T A143849 825155821714086784897292716543, %U A143849 -6468873315977272230111786035347284128217298704834756326835199 %N A143849 Let x(1) = 1 and x(n) = x(n-1)^2 + i for n>1; a(n) is the imaginary part of x(n). %F A143849 a(n+1) = 2*a(n)*A143848(n) + 1. %e A143849 The x(n) sequence starts 1, 1+i, 3*i, -9+i, 80-17*i, 6111-2719*i, ... %Y A143849 A143848 gives the read part of x(n). %K A143849 sign %O A143849 1,3 %A A143849 _Reinhard Zumkeller_, Sep 03 2008 %E A143849 Definition clarified by _N. J. A. Sloane_, Jul 11 2024 at the suggestion of _Harvey P. Dale_.