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 A283416 #13 Jan 11 2020 15:57:47 %S A283416 1,1,2,8,43,405 %N A283416 Number of possible connected steric graphs with n nodes of degree less than 5. %C A283416 This gives the number of hypothetical neutrally charged saturated carbon allotropes and hydrocarbons (alkanes, cycloalkanes, alkyl-cycloalkanes) with n carbon atoms satisfying the octet rule counting all isomers, except conformers. %C A283416 Steric (three-dimensional) graphs can be represented as two-dimensional graphs provided that stereoisomers are taken into account. This means acting the group S_4 on the stereocenters (nodes with 4 different substituents) of each 2D graph and counting all of the resulting non-symmetric molecules. %C A283416 Many of those "theoretical" molecules are to be discovered and some may not exist due to their strained geometries. %C A283416 The terms of this sequence (and related ones) were found by drawing and counting the molecules in the PDFs below. If there are any missing molecules you can contact me. I'll add them in the PDF and update the data section. %H A283416 Natan Arie' Consigli, <a href="/A283416/a283416.pdf">Illustration of a(5) and a(6)</a> %e A283416 a(4) = 8 because there are eight structures with 4 nodes (carbons) following the above rules: butane, isobutane, cyclobutane, methylcyclopropane, (r,r)-bicyclobutane, (s,s)-bicyclobutane, (r,r,r)-tetrahedrane, (s,s,s)-tetrahedrane. %Y A283416 Row sums of A280013. %K A283416 nonn,more,hard %O A283416 1,3 %A A283416 _Natan Arie Consigli_, Mar 07 2017