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 A336994 #12 Aug 16 2020 13:53:17
%S A336994 0,4,16,52,160,9232,13120,39364,41524,250504,1276936,6810136,8153620,
%T A336994 27114424,50143264,106358020,121012864,593279152,1570824736,
%U A336994 2482111348,2798323360,17202377752
%N A336994 Entries of A336938 without duplicates.
%C A336994 Is this (apart from the first 2 entries) the same as A006885? - _R. J. Mathar_, Aug 16 2020
%o A336994 (PARI) firstMiss(A) = { my(i); if(#A == 0 || A[1] > 0, return(0)); for(i = 1, A[#A] + 1, if(!setsearch(A, i), return(i))); };
%o A336994 iter(A) = { my(a = firstMiss(A)); while(!setsearch(A, a), A = setunion(A, Set([a])); a = if(a % 2, 3*a+1, a/2)); A; };
%o A336994 makeVec(m) = { my(v = [], A = Set([0]), i); for(i = 1, m, if (length(v) == 0 || v[length(v)] != A[#A], v = concat(v, A[#A])); if (i < m, A = iter(A))); v; };
%o A336994 makeVec(10000)
%Y A336994 Cf. A336938.
%K A336994 nonn,more
%O A336994 1,2
%A A336994 _Markus Sigg_, Aug 10 2020
%E A336994 a(16)-a(22) from _Jinyuan Wang_, Aug 13 2020