A121950 Number of isomeric aza-benzenoids with two nitrogen atoms and n hexagons.

3, 10, 48, 243, 1326, 7349, 41030, 228694, 1270663, 7031737

Offset

1,1

Links

Table of n, a(n) for n=1..10.

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

Cf. A018190, A121949, A121951, A121952, A121972, A121973, A121975, A121974.

Sequence in context: A140964 A368553 A220362 * A005921 A193281 A367754

Adjacent sequences: A121947 A121948 A121949 * A121951 A121952 A121953

Keyword

nonn,more

Author

Parthasarathy Nambi, Sep 04 2006

Extensions

a(1) corrected by Andrey Zabolotskiy, Nov 19 2023

Status

approved