A079140 Numbers n such that (Product of first n twin prime pair averages [A014574]) - 1 is prime.

1, 2, 7, 11, 16, 32, 402, 1107, 1829, 2584, 3124, 6936

Offset

1,2

Comments

Some of the larger entries may only correspond to probable primes.

Links

Table of n, a(n) for n=1..12.

Example

a(2) = 2 because the product of the first two terms of A014574 - 1, 4 * 6-1 = 23, 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) {atm(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: A190518 A190750 A049635 * A357843 A176897 A362770

Adjacent sequences: A079137 A079138 A079139 * A079141 A079142 A079143

Keyword

nonn,more

Author

Jason Earls, Dec 26 2002

Extensions

a(8)-a(12) from Amiram Eldar, Dec 14 2019

Status

approved