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 A307233 #9 May 13 2019 22:03:21
%S A307233 0,1,0,1,3,3,0,1,0,9,3,9,0,7,12,1,3,9,0,1,0,9,3,9,18,13,0,21,3,9,0,1,
%T A307233 27,9,7,9,0,19,0,1,3,21,0,37,18,9,3,33,0,49,27,13,3,27,12,49,0,9,3,21,
%U A307233 0,31,0,1,13,3,0,13,27,49,3,9,0,37,57,57,42
%N A307233 a(n) = Product_{k=1..n} (k^2 + k + 1) mod n.
%F A307233 a(n) = A130032(n) mod n.
%F A307233 If prime p == 1 mod 3, a(p) = 0; if p == 2 mod 3, a(p) = 3 for prime p > 3.
%F A307233 a(A002061(k)) = 0.
%F A307233 If a(j) = a(k) = 0, then a(j*k) = 0.
%e A307233 a(4) = 1 since 3*7*13*21 = 1 mod 4.
%t A307233 Table[Mod[Product[k^2+k+1, {k, 0, n}], n], {n, 1, 100}]
%o A307233 (PARI) a(n) = prod(k=1, n, k^2+k+1) % n
%Y A307233 Cf. A002061, A130032.
%K A307233 nonn,easy
%O A307233 1,5
%A A307233 _Jinyuan Wang_, Apr 14 2019