A005961 Number of acyclic disubstituted alkanes with n carbon atoms and identical substituents. (Formerly M1447)

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

1,2

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

Table of n, a(n) for n=1..28.

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.

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

Crossrefs

Cf. A005960.

Sequence in context: A218551 A293297 A318485 * A036249 A126031 A151416

Adjacent sequences: A005958 A005959 A005960 * A005962 A005963 A005964

Keyword

nonn

Author

N. J. A. Sloane

Extensions

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

Status

approved