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A127989
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a(n) = 2*n^3 - 2*n + 9.
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4
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9, 21, 57, 129, 249, 429, 681, 1017, 1449, 1989, 2649, 3441, 4377, 5469, 6729, 8169, 9801, 11637, 13689, 15969, 18489, 21261, 24297, 27609, 31209, 35109, 39321, 43857, 48729, 53949, 59529, 65481, 71817, 78549, 85689, 93249, 101241, 109677, 118569
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OFFSET
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1,1
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COMMENTS
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All numbers generated by the irreducible polynomial 2*n^3-2*n+9 are composite (indeed, they are multiples of 3). Largest prime factor A127990, smallest prime factor A127991, number of prime factors A127992.
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LINKS
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FORMULA
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a(n) = 2*(n-1)*n*(n+1)+9 = 3*(2*A007290(n+1)+3).
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MATHEMATICA
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Table[2x^3 - 2x + 9, {x, 1, 100}]
LinearRecurrence[{4, -6, 4, -1}, {9, 21, 57, 129}, 50] (* G. C. Greubel, May 08 2018 *)
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PROG
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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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