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 A292050 #8 Oct 01 2017 00:05:43
%S A292050 1,2,3,4,5,6,7,9,10,11,13,14,15,17,21,22,23,25,26,29,31,33,34,35,39,
%T A292050 41,43,46,47,49,51,55,58,59,62,65,69,73,77,79,82,83,85,86,87,91,93,94,
%U A292050 97,101,109,115,118,119,121,123,127,129,137,139,141,143,145
%N A292050 Matula-Goebel numbers of semi-binary rooted trees.
%C A292050 An unlabeled rooted tree is semi-binary if all out-degrees are <= 2. The number of semi-binary trees with n nodes is equal to the number of binary trees with n+1 leaves; see A001190.
%t A292050 nn=200;
%t A292050 primeMS[n_]:=If[n===1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
%t A292050 semibinQ[n_]:=Or[n===1,With[{m=primeMS[n]},And[Length[m]<=2,And@@semibinQ/@m]]];
%t A292050 Select[Range[nn],semibinQ]
%Y A292050 Cf. A000081, A001190, A007097, A036656, A061773, A111299, A214577, A291636.
%K A292050 nonn
%O A292050 1,2
%A A292050 _Gus Wiseman_, Sep 08 2017