A079139 Numbers n such that (Product of first n twin prime pair averages [A014574] ) + 1 is prime.

1, 5, 45, 218, 506, 538, 1027

Offset

1,2

Comments

a(3) and a(4) certified prime with Primo.

Links

Table of n, a(n) for n=1..7.

Example

a(2) = 5 because the product of the first five terms of A014574 + 1, 4*6*12*18*30 + 1 = 155521, is prime.

Mathematica

seq = {1}; prod = 4; k = 1; Do[If[AllTrue[6 n + {-1, 1}, PrimeQ], prod *= 6 n; k++; If[PrimeQ[prod + 1], AppendTo[seq, k]]], {n, 1, 5000}]; seq (* Amiram Eldar, Dec 14 2019 *)

Prog

(PARI) { atp(N)= local(t, c); t=1; c=0; forprime(p=2, N, if(isprime(p+2), t*=p+1; c++; if(isprime(t+1), print1(c, ", ")))) }

Crossrefs

Cf. A014574.

Sequence in context: A201876 A351426 A027801 * A269911 A249638 A188349

Adjacent sequences: A079136 A079137 A079138 * A079140 A079141 A079142

Keyword

nonn,more

Author

Jason Earls, Dec 26 2002

Extensions

a(7) from Amiram Eldar, Dec 14 2019

Status

approved