A121950 Number of isomeric aza-benzenoids with two nitrogen atoms and n hexagons.
3, 10, 48, 243, 1326, 7349, 41030, 228694, 1270663, 7031737
Offset: 1
Examples
In a single hexagon (benzene), any 2 of the 6 carbon atoms can be chosen to be replaced by nitrogen, and it can be done in 3 ways, obtaining pyridazine, pyrimidine, or pyrazine, so a(1) = 3. For a(2) = 10, see the corresponding column of Table 7 from Trinajstić et al.
Links
- N. Trinajstić, Ž. Jeričević, J. V. Knop, W. R. Müller and K. Szymanski, Computer generation of isomeric structures, Pure and Appl. Chem., vol. 55 (1983) pp. 379-390. See Table 6 on p. 387.
Extensions
a(1) corrected by Andrey Zabolotskiy, Nov 19 2023