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 A261336 #15 Jul 26 2022 22:03:05 %S A261336 0,0,0,1,3,10,30,88,255,742,2157,6312,18563,54932,163479,489264, %T A261336 1471692,4447896,13500689,41140608,125818217,386050543,1188093392, %U A261336 3666547089,11344058829,35180323336,109339097119,340508394528 %N A261336 Number of achiral molecules containing two linear or branched chiral alkyl chains of n carbon atoms each. %C A261336 a(n) is half the number of chiral planted trees of n nodes (A005628(n)). This number is half the total number of chiral alkanes because the two alkyl chains are required to have the same length with opposite chirality at each chiral center: For each chiral alkane, there is only one other with opposite chirality at each center. The two alkyl chains are attached to a scaffold with a mirror plane between them, thus imparting achirality on the whole molecule. Although such a molecule contains chiral centers, the molecule itself is not chiral--its mirror image is superposable on itself. These compounds are called meso compounds in chemistry. %H A261336 Matthew S. MacLennan, <a href="http://physicallychemist.blogspot.ca/2015/07/on-number-of-phthalates.html">On the Number of Phthalates</a>, Physically Chemist Blog, 17 July 2015. %F A261336 a(n) = A005628(n) / 2. %Y A261336 Equals half A005628. %K A261336 nonn %O A261336 1,5 %A A261336 _Matthew S. MacLennan_, Aug 15 2015