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A165186
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a(n) = Sum_{k=1..n} (k*(n-k) mod n).
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0
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0, 1, 4, 6, 10, 17, 28, 36, 30, 45, 66, 82, 78, 105, 140, 136, 136, 141, 190, 230, 238, 253, 322, 380, 250, 325, 360, 434, 406, 505, 558, 592, 572, 561, 700, 678, 666, 741, 910, 980, 820, 917, 946, 1122, 1050, 1173, 1316, 1432, 1078, 1125, 1394, 1430, 1378, 1449
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OFFSET
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1,3
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COMMENTS
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Comment from Max Alekseyev, Nov 22 2009: For a prime p==3 (mod 4), a(p) = p*h(-p) + p*(p-1)/2 where h(-p) is the class number (listed in A002143). For example, h(-19)=1 and a(19) = 19*1 + 19*18/2 = 190.
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LINKS
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MATHEMATICA
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Table[Sum[Mod[k (n-k), n], {k, n}], {n, 100}]
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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