A338589 - OEIS

%I #10 Nov 22 2020 21:32:44

%S 0,1,2,3,5,10,14,18,15,25,33,41,39,56,70,68,68,75,95,115,119,132,161,

%T 190,125,169,180,217,203,260,279,296,286,289,350,339,333,380,455,490,

%U 410,469,473,561,525,598,658,716,539,575,697,715,689,738,880,966,836,841,944,1105,915

%N Sum of the remainders (s*t mod n), where s + t = n and 1 <= s <= t.

%F a(n) = Sum_{i=1..floor(n/2)} ( i*(n-i) mod n ).

%e a(6) = 10; ((1*5) mod 6) + ((2*4) mod 6) + ((3*3) mod 6) = 5 + 2 + 3 = 10.

%t Table[Sum[Mod[i (n - i), n], {i, Floor[n/2]}], {n, 80}]

%K nonn

%O 1,3

%A _Wesley Ivan Hurt_, Nov 07 2020