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A032801
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Number of unordered sets a,b,c,d of distinct integers from 1..n such that a+b+c+d=0 (mod n).
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0
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0, 0, 0, 0, 1, 3, 5, 9, 14, 22, 30, 42, 55, 73, 91, 115, 140, 172, 204, 244, 285, 335, 385, 445, 506, 578, 650, 734, 819, 917, 1015, 1127, 1240, 1368, 1496, 1640, 1785, 1947, 2109, 2289, 2470, 2670, 2870, 3090
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,6
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REFERENCES
| Barnes, Acta Arith., 5 (1958), p. 65.
E. V. McLaughlin, Numbers of factorizations in non-unique factorial domains, Senior Thesis, Allegeny College, Meadville, PA, April 2004.
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MAPLE
| f := n-> if n mod 2 <> 0 then (n-1)*(n-2)*(n-3)/24 elif n mod 4 = 0 then (n-4)*(n^2-2*n+6)/24 else (n-2)*(n^2-4*n+6)/24; fi;
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CROSSREFS
| Sequence in context: A081946 A166709 A053618 * A033818 A120452 A144116
Adjacent sequences: A032798 A032799 A032800 * A032802 A032803 A032804
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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