The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A221042 The Wiener index of the Bethe cactus lattice graph D_n defined pictorially in the Hosoya - Balasubramanian reference. 1
 8, 212, 3632, 50504, 624632, 7190492, 78973664, 839594768, 8717571176, 88915009892, 894366753296, 8896551656792, 87694439633240, 857879937077612, 8338591552929728, 80606380453484576, 775488956137204424, 7429684469671844852, 70919715248730034160, 674750433200813750120 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES K. Balasubramanian, Recent developments in tree-pruning methods and polynomials for cactus graphs and trees, J. Math. Chemistry, 4 (1990) 89-102. H. Hosoya, K. Balasubramanian, Exact dimer statistics and characteristic polynomials of cacti lattices, Theor. Chim. Acta 76 (1989) 315-329. LINKS FORMULA a(n) = (1/2)+3^n*(3*n+4)+3^(2*n)*(3*n-9/2). G.f.: 4*x*(2+3*x+27*x^2)/((1-x)*(1-3*x)^2*(1-9*x)^2). - Bruno Berselli, Dec 30 2012 MAPLE a := proc (n) options operator, arrow: 1/2+3^n*(3*n+4)+3^(2*n)*(3*n-9/2) end proc: seq(a(n), n = 1 .. 20); CROSSREFS Cf. A221043. Sequence in context: A197767 A024288 A081794 * A247032 A027646 A224096 Adjacent sequences:  A221039 A221040 A221041 * A221043 A221044 A221045 KEYWORD nonn,easy AUTHOR Emeric Deutsch, Dec 30 2012 STATUS approved

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

Last modified November 29 21:32 EST 2021. Contains 349416 sequences. (Running on oeis4.)