OFFSET
0,3
COMMENTS
Form a graph from a triangle and its midpoint triangle. A093045 counts walks of length n between a vertex of the original triangle and the opposite vertex of the midpoint triangle.
LINKS
Index entries for linear recurrences with constant coefficients, signature (1,7,2,-4).
FORMULA
G.f.: 2x^2(1+x)/((1+x-x^2)(1-2x-4x^2));
a(n) = 2(2^n/6+(-1)^n/3)(((1+sqrt(5))/2)^n/sqrt(5)-((1-sqrt(5))/2)^n/sqrt(5)).
a(n) = 2*A093122(n-1). - R. J. Mathar, Dec 17 2014
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Mar 22 2004
STATUS
approved