A136351 Primorial numbers p# such that p# + 1 is a prime.

1, 2, 6, 30, 210, 2310, 200560490130

Offset: 1

Author

Enoch Haga, Dec 25 2007

Keywords

• easy
• nonn

Comments

This sequence is different from A121069 and A002110.

a(8) = A002110(75) has 154 digits and is too long to be listed. - R. J. Mathar, Jul 23 2008

Examples

			a(6)=2310 is followed by prime 2311 whereas 30030 is not followed by a prime.
		

Links

• James C. McMahon, Table of n, a(n) for n = 1..10 (a(n) for n = 2..10 by Miles Englezou).

Crossrefs

Cf. A002110, A014545, A018239, A121069, A136349, A136350, A136352.

Programs

Mathematica

Select[FoldList[Times, 1, Prime[Range[18]]],PrimeQ[#+1]&] (* James C. McMahon, May 08 2025 *)

PARI

S=[];for(n=0, 80, k=vecprod(primes(n)); if(isprime(k+1), S=concat(S,k))); S \\ Miles Englezou, Oct 28 2024

Formula

{A002110(j): A002110(j)+1 in A000040}. - R. J. Mathar, Jul 23 2008

a(n) = A002110(A014545(n)). - Michel Marcus, Apr 05 2021

a(n) = A018239(n) - 1. - James C. McMahon, May 08 2025

Extensions

Changed a(1) from 4 to 2 and edited by R. J. Mathar, Jul 23 2008

a(1)=1 inserted by James C. McMahon, May 08 2025