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A165220
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Numbers n such that 8*n+1 is a cube.
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1
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0, 91, 614, 1953, 4492, 8615, 14706, 23149, 34328, 48627, 66430, 88121, 114084, 144703, 180362, 221445, 268336, 321419, 381078, 447697, 521660, 603351, 693154, 791453, 898632, 1015075, 1141166, 1277289, 1423828, 1581167, 1749690, 1929781
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OFFSET
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0,2
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COMMENTS
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For every even n, n^4+(n/2)^3 is a cube.
In effect, a(n) = n*(24*n+3+64*n^2) and 8*a(n)+1 = (8*n+1)^3. [R. J. Mathar, Oct 18 2010]
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LINKS
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FORMULA
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G.f.: x*(91+250*x+43*x^2)/(1-x)^4. [Colin Barker, Jun 15 2012]
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MATHEMATICA
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LinearRecurrence[{4, -6, 4, -1}, {0, 91, 614, 1953}, 100] (* Vincenzo Librandi, Apr 06 2013 *)
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PROG
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(Magma) I:=[0, 91, 614, 1953]; [n le 4 select I[n] else 4*Self(n-1)-6*Self(n-2)+4*Self(n-3)-Self(n-4): n in [1..50]]; // Vincenzo Librandi, Apr 06 2013
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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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EXTENSIONS
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STATUS
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approved
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