0,3

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.

G.f.: 2x^2(1+x)/((1+x-x^2)(1-2x-4x^2)); a(n)=2*A001045(n-1)*A000045(n); a(n)=2(2^n/6+(-1)^n/3)(((1+sqrt(5))/2)^n/sqrt(5)-((1-sqrt(5))/2)^n/sqrt(5)).

Sequence in context: A151449 A045664 A106520 this_sequence A083694 A009679 A007727

Adjacent sequences: A093042 A093043 A093044 this_sequence A093046 A093047 A093048

easy,nonn

Paul Barry (pbarry(AT)wit.ie), Mar 22 2004