A110159 a(n) = (n+1)(n+2)(n+3)(9n^2 + 26n + 20)/120.

1, 11, 54, 179, 469, 1050, 2100, 3858, 6633, 10813, 16874, 25389, 37037, 52612, 73032, 99348, 132753, 174591, 226366, 289751, 366597, 458942, 569020, 699270, 852345, 1031121, 1238706, 1478449, 1753949, 2069064, 2427920, 2834920, 3294753

Offset

0,2

Comments

Kekulé numbers for certain benzenoids.

References

S. J. Cyvin and I. Gutman, Kekulé structures in benzenoid hydrocarbons, Lecture Notes in Chemistry, No. 46, Springer, New York, 1988 (pp. 167-170, Table 10.5/II/6).

Links

Table of n, a(n) for n=0..32.

Index entries for linear recurrences with constant coefficients, signature (6,-15,20,-15,6,-1).

Formula

G.f.: (1 + 5x + 3x^2)/(1-x)^6.

a(n) = Sum_{i=0..n} (i+1)*Sum_{j=n-i+1..n+1} A000217(j). - J. M. Bergot and Robert Israel, Aug 29 2022

Maple

a:=n->(n+1)*(n+2)*(n+3)*(9*n^2+26*n+20)/120: seq(a(n), n=0..35);

Crossrefs

Cf. A000217.

Sequence in context: A003867 A059135 A213840 * A309921 A061983 A079884

Adjacent sequences: A110156 A110157 A110158 * A110160 A110161 A110162

Keyword

nonn,easy

Author

Emeric Deutsch, Nov 18 2005

Status

approved