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A007773
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For any circular arrangement of 0..n-1, let S = sum of squares of every sum of two contiguous numbers; then a(n) = # of distinct values of S.
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3
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1, 1, 1, 3, 8, 21, 43, 69, 102, 145, 197, 261, 336, 425, 527, 645, 778, 929, 1097, 1285, 1492, 1721, 1971, 2245, 2542, 2865, 3213, 3589, 3992, 4425, 4887, 5381, 5906, 6465, 7057, 7685, 8348, 9049, 9787, 10565, 11382, 12241, 13141, 14085, 15072, 16105
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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LINKS
| K. S. Brown, The Dartboard Sequence
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FORMULA
| For n >= 7, a(n) = (n^3-16n+27)/6 (n odd); (n^3-16n+30)/6 (n even).
G.f.: x*(1-2*x+4*x^3+3*x^5-10*x^7+2*x^8+8*x^9-4*x^10)/((1-x)^3*(1-x^2)) - Michael Somos, May 03, 2002
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PROG
| (PARI) a(n)=polcoeff(x*(1-2*x+4*x^3+3*x^5-10*x^7+2*x^8+8*x^9-4*x^10+O(x^n))/(1-x)^3/(1-x^2), n)
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CROSSREFS
| Sequence in context: A103736 A172243 A101332 * A071078 A179903 A193045
Adjacent sequences: A007770 A007771 A007772 * A007774 A007775 A007776
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KEYWORD
| nonn,easy
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AUTHOR
| K. S. Brown [ kevin2003(AT)delphi.com ], Hugh L. Montgomery
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EXTENSIONS
| More terms from David W. Wilson (davidwwilson(AT)comcast.net), Oct 27 2000
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