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a(n) = n - A305211(n).
1

%I #26 May 22 2020 07:21:55

%S 0,0,0,0,0,0,2,0,4,0,0,0,0,4,0,0,0,8,0,0,6,0,0,0,0,0,12,8,0,0,0,0,0,0,

%T 10,16,0,0,0,0,0,12,0,0,20,0,0,0,14,0,0,0,0,24,0,16,0,0,0,0,0,0,38,0,

%U 0,0,0,0,0,20,0,32,0,0,0,0,22,0,0,0,36,0,0

%N a(n) = n - A305211(n).

%C Number of integers d from 0 to n-1 such that x^3 + y^3 == d (mod n) has no solutions in integers.

%o (Python) [n-len(set((pow(x,3,n)+pow(y,3,n))%n for x in range(n) for y in range(x+1))) for n in range(1,51)]

%o (PARI) a(n) = my(v=[]); for (x=1, n, for (y=1, n, v = concat(v, Mod(x, n)^3 + Mod(y, n)^3))); n - #Set(v); \\ _Michel Marcus_, Jul 10 2018

%Y Cf. A305211.

%K nonn

%O 1,7

%A _Jack Zhang_, May 27 2018

%E a(50)-a(83) from _Jon E. Schoenfield_, May 28 2018