OFFSET
1,2
EXAMPLE
a(2) is not 2 since 1*2-1 = 1 is not prime, but 1*3-1 = 2 is prime, hence a(2) = 3.
a(6) is not 2 since 2*2*2*2-1 = 15 is not prime, but 2*3-1 = 5, 2*2*3-1 = 11, 2*2*2*3-1 = 23, 3*2*2*2*3-1 = 71 are all prime, hence a(6) = 3.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Amarnath Murthy, Jun 24 2004
EXTENSIONS
Edited and extended by Klaus Brockhaus, Jul 05 2004
a(10) from Donovan Johnson, Apr 22 2008
a(11)-a(12) from Bert Dobbelaere, Jan 13 2020
STATUS
approved