0,3

a(n)=trace(A^n)/6 where A is the adjacency matrix of the graph obtained by constructing external triangles on the sides of a triangle (or equivalently, taking a triangle and its midpoint triangle). A Lucas Jacobsthal product. Compare with A093042.

Table of n, a(n) for n=0..26.

Index entries for linear recurrences with constant coefficients, signature (1,7,2,-4).

G.f. : (1-x-4x^2-x^3)/((1-2x-4x^2)(1+x-x^2)); a(n)=L(n)*A078008(n)/2=A000034(n)*A078008(n)/2.

Sequence in context: A254884 A034475 A156173 * A081698 A182096 A012123

Adjacent sequences: A094629 A094630 A094631 * A094633 A094634 A094635

easy,nonn

Paul Barry, May 16 2004

approved