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URL: https://oeis.org/A091424

⇱ A091424 - OEIS

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A091424
Numbers m such that m#*2^m + 1 is prime, where m# = A002110(m).
1
1, 3, 4, 6, 10, 30, 31, 98, 156, 230, 432, 490, 1623, 1666, 9324, 9693
OFFSET
1,2
COMMENTS
1# = 2, 2# = 2*3 = 6, 3# = 2*3*5 = 30.
No more terms < 5000. - L. Joris Perrenet, Mar 17 2020
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)=my(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)), print1(i, ", ")))
CROSSREFS
Sequence in context: A103016 A061032 A391267 * A092839 A185874 A320688
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
a(15)-a(16) from Michael S. Branicky, Aug 31 2024
STATUS
approved