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A011868
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a(n) = floor(n*(n-1)/15).
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0
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0, 0, 0, 0, 0, 1, 2, 2, 3, 4, 6, 7, 8, 10, 12, 14, 16, 18, 20, 22, 25, 28, 30, 33, 36, 40, 43, 46, 50, 54, 58, 62, 66, 70, 74, 79, 84, 88, 93, 98, 104, 109, 114, 120, 126, 132, 138, 144, 150, 156, 163, 170, 176, 183, 190, 198, 205, 212, 220, 228, 236, 244, 252
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OFFSET
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0,7
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LINKS
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Index entries for linear recurrences with constant coefficients, signature (2,-1,0,0,0,0,0,0,0,0,0,0,0,0,1,-2,1).
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FORMULA
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a(n) = 2*a(n-1) - a(n-2) + a(n-15) - 2*a(n-16) + a(n-17).
G.f.: x^5*(1+x^2*(-1+x*(1+x^2*(1+x*(-1+x^2)))))/(1+x*(-2+x*(1+x^13*(-1+(2-x)*x)))). (End)
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MATHEMATICA
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LinearRecurrence[{2, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -2, 1}, {0, 0, 0, 0, 0, 1, 2, 2, 3, 4, 6, 7, 8, 10, 12, 14, 16}, 63] (* Georg Fischer, Aug 15 2021 *)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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