The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A109108 a(n) = 10a(n-1) + a(n-2), a(0)=1, a(1)=9. 0
 1, 9, 91, 919, 9281, 93729, 946571, 9559439, 96540961, 974969049, 9846231451, 99437283559, 1004219067041, 10141627953969, 102420498606731, 1034346614021279, 10445886638819521, 105493213002216489 (list; graph; refs; listen; history; text; internal format)
 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 (p. 284, K{Q_1(n)}). LINKS Table of n, a(n) for n=0..17. Tanya Khovanova, Recursive Sequences Index entries for linear recurrences with constant coefficients, signature (10,1). FORMULA a(n) = (1/2/sqrt(26))((sqrt(26)+4)(5+sqrt(26))^n+(sqrt(26)-4)(5-sqrt(26))^n). G.f.: (1-z)/(1-10z-z^2). MAPLE a:=n->(1/2/sqrt(26))*((sqrt(26)+4)*(5+sqrt(26))^n+(sqrt(26)-4)*(5-sqrt(26))^n): seq(expand(a(n)), n=0..20); MATHEMATICA LinearRecurrence[{10, 1}, {1, 9}, 20] (* Harvey P. Dale, Jan 04 2024 *) CROSSREFS First differences of A041041. Sequence in context: A015585 A366393 A242299 * A163456 A318593 A362728 Adjacent sequences: A109105 A109106 A109107 * A109109 A109110 A109111 KEYWORD nonn,easy AUTHOR Emeric Deutsch, Jun 19 2005 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified July 23 15:54 EDT 2024. Contains 374552 sequences. (Running on oeis4.)