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 A283616 #32 Mar 03 2024 10:15:34
%S A283616 1,1,2,1,0,2,1,0,4,4,0,6,0,0,8,1,0,0,4,0,12,3,0,20,0,0,24,0,0,24,5,0,
%T A283616 0,32,0,16,9,0,0,56,0,72,0,0,320,0,0,0,84,0,24,240,0,512,160,0,90,0,0,
%U A283616 0,0,0,0,12,0,500,0,0,160,672,0,0,0,0,2880,1792,0,0,72,0,0,378
%N A283616 a(n) = Product_{k=2..floor(sqrt(2n-1)/2)+1} (2n-1) mod (2k-1).
%C A283616 For n>1, if a(n) > 0 then 2n-1 is prime.
%C A283616 From _Robert G. Wilson v_, Mar 15 2017: (Start)
%C A283616 Except for n=1, a(n)=0 iff 2n-1 is not prime (A104275).
%C A283616 a(n) is prime for n: 3, 6, 22 & 31. (End)
%H A283616 Charles R Greathouse IV, <a href="/A283616/b283616.txt">Table of n, a(n) for n = 1..10000</a>
%t A283616 Table[Product[Mod[(2 n - 1), (2 k - 1)], {k, 2, Floor[Sqrt[2 n - 1]/2] + 1}], {n, 80}] (* _Michael De Vlieger_, Mar 15 2017 *)
%o A283616 (PARI) a(n)=my(t=2*n-1); prod(k=2,sqrtint(t\4)+1, t%(2*k-1)) \\ _Charles R Greathouse IV_, Mar 22 2017
%Y A283616 Cf. A180491.
%K A283616 nonn
%O A283616 1,3
%A A283616 _Zhandos Mambetaliyev_, Mar 11 2017