This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A305212 #26 May 22 2020 07:21:55 %S A305212 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 A305212 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 A305212 0,0,0,0,0,20,0,32,0,0,0,0,22,0,0,0,36,0,0 %N A305212 a(n) = n - A305211(n). %C A305212 Number of integers d from 0 to n-1 such that x^3 + y^3 == d (mod n) has no solutions in integers. %o A305212 (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 A305212 (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 A305212 Cf. A305211. %K A305212 nonn %O A305212 1,7 %A A305212 _Jack Zhang_, May 27 2018 %E A305212 a(50)-a(83) from _Jon E. Schoenfield_, May 28 2018