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A127989
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Numbers of the form 2*n^3-2*n+9.
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2
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| All numbers generated by the irreducible polynomial 2*n^3-2*n+9 are composite. Largest prime factor A127990, smallest prime factor A127991, number of prime factors A127992.
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LINKS
| Vincenzo Librandi, Table of n, a(n) for n = 1..10000
Index to sequences with linear recurrences with constant coefficients, signature (4,-6,4,-1).
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FORMULA
| a(n) = 2*(n-1)*n*(n+1)+9 = 3*(2*A007290(n+1)+3).
G.f.: 3*x*(3-5*x+9*x^2-3*x^3)/(1-x)^4. - Bruno Berselli, Sep 09 2011
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MATHEMATICA
| Table[2x^3 - 2x + 9, {x, 1, 100}]
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PROG
| (MAGMA) [2*(n-1)*n*(n+1)+9: n in [1..50]]; // Vincenzo Librandi, Sep 13 2011
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CROSSREFS
| Cf. A127990, A127991, A127992.
Sequence in context: A176896 A134717 A147169 * A147337 A020290 A020288
Adjacent sequences: A127986 A127987 A127988 * A127990 A127991 A127992
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KEYWORD
| nonn,easy
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AUTHOR
| Artur Jasinski (grafix(AT)csl.pl), Feb 10 2007
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