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A213775
Principal diagonal of the convolution array A213774.
3
1, 11, 38, 97, 213, 432, 833, 1555, 2838, 5097, 9045, 15904, 27761, 48171, 83174, 143009, 244997, 418384, 712465, 1210195, 2050966, 3468681, 5855333, 9867072, 16600993, 27889547, 46790438, 78401185, 131212533, 219355632
OFFSET
1,2
FORMULA
a(n) = 4*a(n-1) - 4*a(n-2) - 2*a(n-3) + 4*a(n-4) - a(n-6).
G.f.: f(x)/g(x), where f(x) = x*(1 + 7*x - 2*x^2 - 9*x^3 - 5*x^4) and g(x) = (1 - 2*x + x^3 )^2.
MATHEMATICA
(See A213774.)
CROSSREFS
Sequence in context: A143109 A007585 A024202 * A133258 A288745 A103738
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Jun 21 2012
STATUS
approved