OFFSET
1,1
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.
EXAMPLE
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.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Parthasarathy Nambi, Sep 04 2006
EXTENSIONS
a(1) corrected by Andrey Zabolotskiy, Nov 19 2023
STATUS
approved