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A289870
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a(n) = n*(n + 1) for n odd, otherwise a(n) = (n - 1)*(n + 1).
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1
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-1, 2, 3, 12, 15, 30, 35, 56, 63, 90, 99, 132, 143, 182, 195, 240, 255, 306, 323, 380, 399, 462, 483, 552, 575, 650, 675, 756, 783, 870, 899, 992, 1023, 1122, 1155, 1260, 1295, 1406, 1443, 1560, 1599, 1722, 1763, 1892, 1935, 2070, 2115, 2256, 2303, 2450, 2499
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OFFSET
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0,2
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COMMENTS
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a(n) is a fifth-order linear recurrence whose main interest is that it is related to (at least) eight other sequences (see the formula section).
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LINKS
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FORMULA
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a(n) = (n + 1)*(n - 1 + (n mod 2)).
G.f.: (1-3*x-3*x^2-3*x^3)/((-1+x)^3*(1+x)^2).
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MATHEMATICA
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a[n_] := (n + 1)(n - 1 + Mod[n, 2]); Table[a[n], {n, 0, 50}]
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PROG
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CROSSREFS
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KEYWORD
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sign,easy
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AUTHOR
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STATUS
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approved
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