OFFSET
1,1
COMMENTS
It appears that the only term that has more than one such representation is 19 = (2^0+1)*(3^2+1)-1 = (2^2+1)*(3^1+1)-1.
LINKS
Robert Israel, Table of n, a(n) for n = 1..1635
EXAMPLE
a(7) = 29 is a term because it is (2^1+1)*(3^2+1)-1 and is prime.
MAPLE
N:= 10^20: # for all terms <= N
S:= {seq(seq((2^a+1)*(3^b+1)-1, b=0..ilog[3]((N+1)/(2^a+1)-1)), a=0..ilog[2]((N-1)/2))}:
sort(convert(select(isprime, S), list));
CROSSREFS
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, Dec 31 2021
STATUS
approved