A165186 a(n) = Sum_{k=1..n} (k*(n-k) mod n).

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

Offset: 1

Author

Wouter Meeussen, Sep 06 2009

Keywords

• nonn

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.

Crossrefs

Cf. A008784, A048153

Programs

Mathematica

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