A005961 Number of acyclic disubstituted alkanes with n carbon atoms and identical substituents.

1, 2, 5, 13, 37, 108, 325, 993, 3070, 9564, 29979, 94392, 298311, 945592, 3005021, 9570559, 30539044, 97611676, 312462096, 1001554565, 3214232129, 10326580526, 33210135104, 106901289420, 344398593149, 1110395171502, 3582666470285, 11567123373968

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn

Comments

Acyclic alkanes of the form C_nH_mX2. - Sean A. Irvine, Nov 12 2016

References

• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

• R. C. Read, The Enumeration of Acyclic Chemical Compounds, pp. 25-61 of A. T. Balaban, ed., Chemical Applications of Graph Theory, Ac. Press, 1976. [Annotated scanned copy] See p. 44.

Crossrefs

Cf. A005960.

Formula

G.f.: -1 + (1/(1-x*B(x)^2) + 1/(1-x*B(x^2)))/2 where B(x) is the g.f. for A000625. - Sean A. Irvine, Nov 12 2016

Extensions

More terms and title improved by Sean A. Irvine, Nov 12 2016