A121254 Number of conjugated cycles composed of six carbons in (n,n)-nanotubes in terms of the number of naphthalene units.

4, 16, 60, 208, 680, 2136, 6524, 19520, 57492, 167240, 481624, 1375536

Offset

1,1

Comments

See Table 2 on page 412 of Lukovits and Janezic paper for details.

Links

Table of n, a(n) for n=1..12.

I. Lukovits et al. Enumeration of conjugated circuits in nanotubes, J. Chem. Inf. Comput. Sci. 44 (2004), 410-414.

Index entries for linear recurrences with constant coefficients, signature (6, -11, 6, -1).

Formula

Conjecture: a(n)=6a(n-1)-11a(n-2)+6a(n-3)-a(n-4)=4*A117202(n). G.f.: 4*x*(1-2*x+2*x^2)/(x^2-3*x+1)^2. [From R. J. Mathar, Mar 18 2009]

Example

If n=5 then the number of conjugated cycles composed of six carbons in (n,n)-nanotubes is 680 which is the fifth term in the sequence. Here n is the number of naphthalene units.

Crossrefs

Sequence in context: A265955 A217374 A055295 * A261519 A262591 A119827

Adjacent sequences: A121251 A121252 A121253 * A121255 A121256 A121257

Keyword

nonn

Author

Parthasarathy Nambi, Aug 22 2006

Status

approved