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 A008879 #26 Jul 08 2025 01:22:13 %S A008879 87,262,131,394,197,592,296,148,74,37,112,56,28,14,7,22,11,34,17,52, %T A008879 26,13,40,20,10,5,16,8,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2, %U A008879 1,4,2,1,4,2,1,4,2,1,4,2,1,4 %N A008879 3x+1 sequence starting at 87. %D A008879 R. K. Guy, Unsolved Problems in Number Theory, E16. %H A008879 Vincenzo Librandi, <a href="/A008879/b008879.txt">Table of n, a(n) for n = 0..200</a> %H A008879 <a href="/index/3#3x1">Index entries for sequences related to 3x+1 (or Collatz) problem</a> %H A008879 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,1). %p A008879 f := proc(n) option remember; if n = 0 then 87; elif f(n-1) mod 2 = 0 then f(n-1)/2 else 3*f(n-1)+1; fi; end; %t A008879 NestList[If[EvenQ[#], #/2, 3# + 1]&, 87, 100] (* _Vincenzo Librandi_, Jul 29 2014 *) %o A008879 (Magma) [n eq 1 select 87 else IsOdd(Self(n-1)) select 3*Self(n-1)+1 else Self(n-1) div 2: n in [1..80]]; // _Vincenzo Librandi_, Jul 29 2014 %Y A008879 Cf. similar sequences listed in A245671. %Y A008879 Row 87 of A347270. %K A008879 nonn %O A008879 0,1 %A A008879 _N. J. A. Sloane_