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A092061
Numbers k such that primorial(k)^2 + 1 is prime.
3
0, 1, 2, 4, 5, 8, 16, 248
OFFSET
1,3
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
MATHEMATICA
Join[{0}, Flatten[Position[FoldList[Times, Prime[Range[250]]]^2, _?(PrimeQ[ #+1]&)]]] (* Harvey P. Dale, Jan 19 2016 *)
PROG
(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(".")))
CROSSREFS
Sequence in context: A045591 A045581 A253426 * A256760 A281646 A240460
KEYWORD
hard,nonn,more
AUTHOR
Mohammed Bouayoun (mohammed.bouayoun(AT)sanef.com), Feb 19 2004
EXTENSIONS
Officially the 0th primorial is 1 (see A002110), so 0 is also a term in this sequence. Dmitry Kamenetsky, Oct 01 2008
STATUS
approved