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 A324040 #10 Oct 20 2022 16:26:22 %S A324040 0,0,2,0,0,5,3,7,12,12,30,51,75,139,232,365,640,1029,1717,2872,4789, %T A324040 7996,13338,22288,36896,61942,102746,170993,286029,476053,793800 %N A324040 Number of vertex labels congruent to 1 modulo 3 of level n of the irregular triangle A324246. %C A324040 a(n) is also the number of vertex labels congruent to 3 modulo 6 of row n of the irregular triangle A324038. %C A324040 This entry is interesting because it determines the number of vertices with out-degree 1 of level n, for n >= 1, of the modified reduced Collatz trees A324038 and A324246. All other vertices have out-degree 2. Hence this sequence determines recursively the number A324039(n) of vertices of label n of these two trees. %F A324040 a(n) = 2*A324039(n) - A324039(n-1), for n >= 1, and a(0) = 0. Implied by the definition of a(n) given in the name. %Y A324040 Cf. A324038, A324039, A324246. %K A324040 nonn,easy %O A324040 0,3 %A A324040 _Nicolas Vaillant_, Philippe Delarue, _Wolfdieter Lang_, May 09 2019