OFFSET
1,1
COMMENTS
The next k in the sequence is > 4261, if it exists.
Note that (b^k - 1)/(b-1) is prime only if k is prime, so all the elements in this sequence must be primes. - Marco Bodrato (marco2007(AT)bodrato.it), Oct 31 2007
a(8) > 20000, if it exists. - Michael S. Branicky, Aug 12 2024
EXAMPLE
(((2*2)^2) - 1)/(2*2 - 1) = 15/3 = 5 is prime so a(1)=2.
MATHEMATICA
Select[Prime[Range[100]], PrimeQ[((2#)^#-1)/(2#-1)]&] (* Harvey P. Dale, Mar 09 2022 *)
PROG
(PARI) lista(nn) = {forprime(n = 2, nn, if (isprime(((2*n)^n-1)/(2*n-1)), print1(n, ", ")); ); } \\ Michel Marcus, Feb 05 2014
CROSSREFS
KEYWORD
more,nonn
AUTHOR
Pierre CAMI, Jan 29 2005
STATUS
approved