A192030 Square array read by antidiagonals: W(n,p) (n>=1, p>=1) is the Wiener index of the graph G(n,p) obtained in the following way: consider n copies of a star tree with p-1 edges, add a vertex to their union, and connect this vertex with the roots of the star trees.

1, 4, 4, 9, 20, 9, 16, 48, 48, 16, 25, 88, 117, 88, 25, 36, 140, 216, 216, 140, 36, 49, 204, 345, 400, 345, 204, 49, 64, 280, 504, 640, 640, 504, 280, 64, 81, 368, 693, 936, 1025, 936, 693, 368, 81, 100, 468, 912, 1288, 1500, 1500, 1288, 912, 468, 100, 121, 580, 1161, 1696, 2065, 2196, 2065, 1696, 1161, 580, 121

Offset

1,2

Comments

W(n,1)=W(1,n)=n^2=A000290(n).

W(n,2)=W(2,n)=A033579(p)=2*n*(3*n-1).

W(p,n)=W(n,p).

Links

Table of n, a(n) for n=1..66.

B. E. Sagan, Y-N. Yeh and P. Zhang, The Wiener Polynomial of a Graph, Internat. J. of Quantum Chem., 60, 1996, 959-969.

Stephan Wagner, A class of trees and its Wiener index, Acta Applic. Mathem. 91 (2) (2006) 119-132.

Formula

W(n,p)=n*p*(2*n*p-n-p+1).

The Wiener polynomial of the graph G(n,p) is a*t+b*t^2+c*t^3+d*t^4, where a=n*p, b=(1/2)*n*(n+p^2-p-1), c=n*(n-1)*(p-1), d=(1/2)*n*(n-1)*(p-1)^2.

Example

W(2,2)=20 because G(2,2) is the path graph with 4 edges; its Wiener index is 4*1+3*2+2*3+1*4=20.
The square array starts:
1,4,9,16,25,36,49,...;
4,20,48,88,140,204,280,...;
9,48,117,216,345,504,693,...;
16,88,216,400,640,936,1288,...;

Maple

W := proc (n, p) options operator, arrow; n*p*(2*n*p-n-p+1) end proc: for n to 11 do seq(W(n-i, i+1), i = 0 .. n-1) end do; # yields sequence in triangular form
W := proc (n, p) options operator, arrow; n*p*(2*n*p-n-p+1) end proc: for n to 7 do seq(W(n, p), p = 1 .. 10) end do; # yields the first 10 entries in each of the first 7 rows

Crossrefs

Cf. A000290, A033579

Sequence in context: A135065 A067553 A112683 * A117879 A334009 A069549

Adjacent sequences: A192027 A192028 A192029 * A192031 A192032 A192033

Keyword

nonn,tabl

Author

Emeric Deutsch, Jun 29 2011

Status

approved