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A093045
2*Jacobsthal(n-1)*Fibonacci(n).
1
0, 0, 2, 4, 18, 50, 176, 546, 1806, 5780, 18810, 60698, 196704, 636090, 2059174, 6662420, 21562002, 69772930, 225795088, 730679922, 2364543390, 7651801300, 24761784522, 80130760714, 259308681408, 839140370250, 2715515523446
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.
FORMULA
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)).
a(n) = 2*A093122(n-1). - R. J. Mathar, Dec 17 2014
CROSSREFS
Sequence in context: A106520 A301802 A318249 * A330432 A317887 A083694
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Mar 22 2004
STATUS
approved