A092061 Numbers k such that primorial(k)^2 + 1 is prime.

0, 1, 2, 4, 5, 8, 16, 248

Offset: 1

Author

Mohammed Bouayoun (mohammed.bouayoun(AT)sanef.com), Feb 19 2004

Keywords

• hard
• nonn
• more

Comments

Numbers k such that A002110(k)^2 + 1 is prime.

The next term is greater than 2600. [Max Alekseyev, Mar 14 2011]

The next term is greater than 6600. - Michael S. Branicky, Aug 01 2024

Programs

Mathematica

Join[{0},Flatten[Position[FoldList[Times,Prime[Range[250]]]^2,?(PrimeQ[ #+1]&)]]] (* _Harvey P. Dale, Jan 19 2016 *)

PARI

primorial(n)=s=1;for(i=1,n,s=s*prime(i));return(s); for (i=1,250,if(isprime(primorial(i)^2+1),print1(i,","),print1(".")))

Extensions

Officially the 0th primorial is 1 (see A002110), so 0 is also a term in this sequence. Dmitry Kamenetsky, Oct 01 2008