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 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS No more terms < 5000. - L. Joris Perrenet, Mar 17 2020 1# = 2 2# = 2*3 = 6 3# = 2*3*5 = 30 LINKS Table of n, a(n) for n=1..14. 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 Cf. A002110. Sequence in context: A103049 A103016 A061032 * A092839 A185874 A320688 Adjacent sequences: A091421 A091422 A091423 * A091425 A091426 A091427 KEYWORD nonn,hard,more AUTHOR Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 02 2004 EXTENSIONS a(13)-a(14) from Chai Wah Wu, Dec 23 2019 STATUS approved

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Last modified March 1 08:00 EST 2024. Contains 370430 sequences. (Running on oeis4.)