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Search: id:A061167
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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
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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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. [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Aug 19 2008]
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LINKS
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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. [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Aug 19 2008]
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EXAMPLE
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a(2)=32-2=30.
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CROSSREFS
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Adjacent sequences: A061164 A061165 A061166 this_sequence A061168 A061169 A061170
Sequence in context: A081779 A069487 A008385 this_sequence A138404 A136381 A042752
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KEYWORD
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easy,nonn
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AUTHOR
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Henry Bottomley (se16(AT)btinternet.com), Apr 18 2001
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