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A165186 Sum(mod(k*(n-k),n); k=1,2,..,n) 0
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

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.

LINKS

Table of n, a(n) for n=1..54.

MATHEMATICA

Table[Sum[Mod[k (n-k), n], {k, n}], {n, 100}]

CROSSREFS

Cf. A008784, A048153

Sequence in context: A032416 A283496 A117149 * A108232 A027976 A108900

Adjacent sequences:  A165183 A165184 A165185 * A165187 A165188 A165189

KEYWORD

nonn

AUTHOR

Wouter Meeussen, Sep 06 2009

STATUS

approved

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Last modified May 29 16:53 EDT 2017. Contains 287252 sequences.