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A105374
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a(n) = 4*n^3 + 4*n.
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6
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0, 8, 40, 120, 272, 520, 888, 1400, 2080, 2952, 4040, 5368, 6960, 8840, 11032, 13560, 16448, 19720, 23400, 27512, 32080, 37128, 42680, 48760, 55392, 62600, 70408, 78840, 87920, 97672, 108120, 119288, 131200, 143880, 157352, 171640, 186768
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OFFSET
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0,2
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COMMENTS
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For n > 1, the number of straight lines with n points in a 4-dimensional hypercube of with n points on each edge is 4n^3 + 12n^2 + 16n + 8, i.e., A105374(n+1).
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LINKS
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FORMULA
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G.f.: 8*x*(1 + x + x^2)/(1-x)^4. - Colin Barker, May 24 2012
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EXAMPLE
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a(5) = 4*5^3 + 4*5 = 500 + 20 = 520.
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MATHEMATICA
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CoefficientList[Series[8*x*(1+x+x^2)/(1-x)^4, {x, 0, 40}], x] (* or *) LinearRecurrence[{4, -6, 4, -1}, {0, 8, 40, 120}, 50] (* Vincenzo Librandi, Jun 26 2012 *)
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PROG
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(Magma) I:=[0, 8, 40, 120]; [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..45]]; // Vincenzo Librandi, Jun 26 2012
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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