OFFSET
1,1
EXAMPLE
a(2)=28 because 28=2*2*7 and 2^7 + 2^7 + 7^7 = 823799, a prime.
CROSSREFS
KEYWORD
nonn
AUTHOR
Jason Earls, Jul 04 2005
EXTENSIONS
More terms from Ryan Propper, Feb 11 2008
STATUS
approved