

A192025


The Wiener index of the doublecomb graph \/_\/_\/...\/_\/ with 3n (n>=1) nodes. The Wiener index of a connected graph is the sum of the distances between all unordered pairs of vertices in the graph.


1



4, 29, 84, 178, 320, 519, 784, 1124, 1548, 2065, 2684, 3414, 4264, 5243, 6360, 7624, 9044, 10629, 12388, 14330, 16464, 18799, 21344, 24108, 27100, 30329, 33804, 37534, 41528, 45795, 50344, 55184, 60324, 65773, 71540, 77634, 84064, 90839, 97968, 105460
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,1


COMMENTS



LINKS



FORMULA

a(n) = n*(3*n^2+12*n7)/2.
G.f.: x*(4+13*x8*x^2)/(1x)^4.


EXAMPLE

a(2)=29 because in the graph \/_\/ there are 5 pairs of nodes at distance 1, 6 pairs at distance 2, and 4 pairs at distance 3 (5*1 + 6*2 + 4*3 = 29).


MAPLE

a := n > (1/2)*n*(3*n^2+12*n7): seq(a(n), n = 1 .. 40);


CROSSREFS



KEYWORD

nonn,easy


AUTHOR



STATUS

approved



