OFFSET
1,1
COMMENTS
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
MAPLE
N:= 10^6: # for terms <= N
P:= select(isprime, [2, seq(i, i=3..floor(sqrt((N+1)/2)), 2)]):
R:= NULL:
for p in P do
for k from 2 do
v:= 2*p^k-1;
if v > N then break fi;
if isprime(v) then R:= R, v fi;
od od:
sort([R]); # Robert Israel, Feb 20 2024
MATHEMATICA
Select[Prime[Range[20000]], !PrimeQ[(#+1)/2]&&Length[FactorInteger[(#+1)/2]]==1&]
PROG
(PARI) is_A178491(n) = isprime(n) & ispower((n+1)/2, , &n) & isprime(n)
CROSSREFS
KEYWORD
nonn
AUTHOR
Farideh Firoozbakht and M. F. Hasler, Oct 09 2010
STATUS
approved