OFFSET
2,2
EXAMPLE
a(7) = 6 as 7*6 + 1 = 43 is a prime and (7 - 1)/6 = 1 is noncomposite.
a(10) = 3 as 10*3 + 1 = 31 and (10 - 1)/3 = 3 both are primes.
CROSSREFS
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Aug 26 2003
EXTENSIONS
Corrected and extended by David Wasserman, Mar 22 2005
STATUS
approved