A283616 a(n) = Product_{k=2..floor(sqrt(2n-1)/2)+1} (2n-1) mod (2k-1).

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, 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, 0, 0, 0, 0, 12, 0, 500, 0, 0, 160, 672, 0, 0, 0, 0, 2880, 1792, 0, 0, 72, 0, 0, 378

Offset: 1

Author

Zhandos Mambetaliyev, Mar 11 2017

Keywords

• nonn

Comments

For n>1, if a(n) > 0 then 2n-1 is prime.

From Robert G. Wilson v, Mar 15 2017: (Start)

Except for n=1, a(n)=0 iff 2n-1 is not prime (A104275).

a(n) is prime for n: 3, 6, 22 & 31. (End)

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A180491.

Programs

Mathematica

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 *)

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