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 A037121 #9 Jul 08 2025 22:01:47 %S A037121 3,142,71,3338,1669,78444,39222,19611,921718,460859,21660374,10830187, %T A037121 509018790,254509395,11961941566,5980970783,281105626802,140552813401, %U A037121 6605982229848,3302991114924,1651495557462 %N A037121 Trajectory of 3 under map n -> 47n+1 if n odd, n->n/2 if n even. %t A037121 NestList[If[EvenQ[#],#/2,47#+1]&,3,30] (* _Harvey P. Dale_, May 05 2014 *) %K A037121 nonn %O A037121 0,1 %A A037121 _N. J. A. Sloane_