A376756 - OEIS

%I #21 Oct 07 2024 03:20:13

%S 1,1,3,3,1,3,7,3,6,1,1,9,13,7,3,10,1,6,19,3,21,1,1,9,15,13,18,27,1,3,

%T 31,10,3,1,7,21,37,19,39,3,1,21,43,3,6,1,1,30,70,15,3,51,1,18,1,27,57,

%U 1,1,9,61,31,60,36,13,3,67,3,3,7,1,21,73,37,45,75,7,39,79,10,45,1,1,81,1,43,3,3,1,6,163,3,93,1,19,30,97

%N Number of pairs 0 <= x <= y <= n-1 such that x^2 + x*y + y^2 == 0 (mod n).

%H Seiichi Manyama, <a href="/A376756/b376756.txt">Table of n, a(n) for n = 1..10000</a>

%o (Python)

%o def A376756(n):

%o     c = 0

%o     for x in range(n):

%o         z = x**2%n

%o         for y in range(x,n):

%o             if not (z+y*(x+y))%n:

%o                 c += 1

%o     return c # _Chai Wah Wu_, Oct 06 2024

%Y Cf. A000086, A046530, A087786, A290731, A376202, A376203, A376755, A376757.

%K nonn

%O 1,3

%A _Tom Duff_ and _N. J. A. Sloane_, Oct 06 2024