A091424 Numbers m such that m#*2^m + 1 is prime, where m# = A002110(m).

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

Links

Table of n, a(n) for n=1..16.

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

Cf. A002110, A091421.

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

a(15)-a(16) from Michael S. Branicky, Aug 31 2024

Status

approved