

A091424


Numbers n such that n#*2^n + 1 is prime, where n# is product of prime numbers (primorial).


0



1, 3, 4, 6, 10, 30, 31, 98, 156, 230, 432, 490, 1623, 1666
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OFFSET

1,2


COMMENTS

1# = 2 2# = 2*3 = 6 3# = 2*3*5 = 30


LINKS



EXAMPLE

a(1)=1 because 1#*2^1 + 1 = 5 is prime
a(2)=3 because 3#*2^3 + 1 = 241 is prime


PROG

(PARI) pp(n)=s=1; for(i=1, n, s=s*prime(i)); return(s); f(n)=pp(n)*2^n +1; for (i=1, 500, if(isprime(f(i)), print(i)))


CROSSREFS



KEYWORD

nonn,hard,more


AUTHOR

Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 02 2004


EXTENSIONS



STATUS

approved



