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 A064685 #12 Jul 11 2025 08:53:58 %S A064685 1,8,6,17,20,15,10,18,13,21,8,16,24,112,19,107,27,14,22,35,110,30,17, %T A064685 105,25,25,12,113,33,33,20,108,28,28,15,103,116,15,23,36,23,111,10,31, %U A064685 31,93,18,106,119,26,26,88,39,101,114,70,13,34,21,34,96,47,109,47,122 %N A064685 Length of orbit of 2n+1 in the 3x+1 problem. %H A064685 <a href="/index/3#3x1">Index entries for sequences related to 3x+1 (or Collatz) problem</a> %F A064685 f(n)= n/2 if n is even, 3n+1 if n is odd; stop if n is 1. %e A064685 E.g. orbit(3) = 3->10->5->16->8->4->2->1, so length of chain = 8. So a(1) = 8. %o A064685 (ARIBAS) function a064685(maxarg: integer); var n: integer; begin for n := 1 to maxarg by 2 do write(length(orbit(n))," "); end; end; a064685(140); (* For definition of function orbit see A064684. *) %K A064685 nonn,easy %O A064685 0,2 %A A064685 _Jon Perry_, Oct 10 2001 %E A064685 More terms from _Klaus Brockhaus_, Oct 13 2001