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 A294689 #30 Feb 16 2025 08:33:51 %S A294689 -17,-25,-37,-55,-82,-41,-61,-91,-136,-68,-34,-17,-25,-37,-55,-82,-41, %T A294689 -61,-91,-136,-68,-34,-17,-25,-37,-55,-82,-41,-61,-91,-136,-68,-34, %U A294689 -17,-25,-37,-55,-82,-41,-61,-91,-136,-68,-34 %N A294689 Collatz cycle of negative numbers starting with -17. %C A294689 This is the longest of the three known cycles of negative numbers under the reduced Collatz transformation x: x=x/2 when x is even, and x=(3x+1)/2 when x is odd. The other two cycles of negative numbers are (-1,-1,-1,...) and (-5,-7,-10,-5,-7,-10,...). Only one cycle of positive numbers is known: (1,2,1,2,...). (0,0,0,...) is also a cycle. %H A294689 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/CollatzProblem.html">Collatz Problem</a> %H A294689 Wikipedia, <a href="https://en.wikipedia.org/wiki/Collatz_conjecture">Collatz conjecture</a> %F A294689 a(1) = -17, a(n+1) = -A123684(abs(a(n))). %F A294689 a(n+11) = a(n). %Y A294689 Positive number transforms are in A014682; the absolute value of negative number transforms can be found in A123684. %K A294689 sign,easy %O A294689 1,1 %A A294689 _Joe Slater_, Nov 07 2017