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A061167
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a(n) = n^5 - n.
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8
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0, 0, 30, 240, 1020, 3120, 7770, 16800, 32760, 59040, 99990, 161040, 248820, 371280, 537810, 759360, 1048560, 1419840, 1889550, 2476080, 3199980, 4084080, 5153610, 6436320, 7962600, 9765600, 11881350, 14348880, 17210340, 20511120, 24299970, 28629120
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OFFSET
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0,3
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COMMENTS
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(b^2+c^2)/(bc+1) is an integer if {b,c} are of the form {0,n}, {n,n^3}, {n^3,n^5-n}, {n^5-n,n^7-2n^3}, {n^7-2n^3,n^9-3n^5+n}, etc. for some n, in which case the division results in n^2. Cf. A052530.
Convolution of A033429 by A033581. - R. J. Mathar, Aug 19 2008
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LINKS
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Vincenzo Librandi, Table of n, a(n) for n = 0..1000
D. Zagier, Problems posed at the St Andrews Colloquium, 1996
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FORMULA
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a(n) = A033455(n+2)*30 = -n*A024002(n) = A000584(n) - n.
O.g.f.: 30x^2(1+x)^2/(1-x)^6. - R. J. Mathar, Aug 19 2008
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EXAMPLE
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a(2) = 32 - 2 = 30.
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MATHEMATICA
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Table[n^5 - n, {n, 0, 40}] (* Vladimir Joseph Stephan Orlovsky, Feb 20 2012 *)
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PROG
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(MAGMA) [n^5-n: n in [0..40]]; // Vincenzo Librandi, May 02 2011
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CROSSREFS
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Sequence in context: A081779 A069487 A008385 * A189495 A138404 A136381
Adjacent sequences: A061164 A061165 A061166 * A061168 A061169 A061170
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KEYWORD
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easy,nonn
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AUTHOR
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Henry Bottomley, Apr 18 2001
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STATUS
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approved
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