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A111586
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G.f.: -x*(1+x+x^2+2*x^3+3*x^4+3*x^5+x^6-x^7-x^9)/((1+x)*(-1+2*x+x^3)).
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1
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0, 1, 2, 5, 12, 28, 62, 136, 299, 661, 1456, 3213, 7085, 15628, 34467, 76021, 167668, 369805, 815629, 1798928, 3967659, 8750949, 19300824, 42569309, 93889565, 207079956, 456729219, 1007348005, 2221775964, 4900281149, 10807910301, 23837596568, 52575474283, 115958858869
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OFFSET
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0,3
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REFERENCES
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V. Vatter, The Enumeration and Structure of Permutation Classes, Ph. D. Dissertation, Rutgers Univ., Math. Dept., 2006.
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LINKS
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FORMULA
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a(n) = 2*a(n-1) + a(n-3) - 2*(-1)^n for n >= 10. - Greg Dresden, May 18 2020
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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