OFFSET
1,3
COMMENTS
16^16+1 = 274177 * 67280421310721 is a semiprime. Where is the next?
a(73) >= 4. - Donovan Johnson, Sep 27 2010
According to factordb there are currently no other known candidates for semiprimes, with 781^781+1 being the largest fully factored number of this form. - Hugo Pfoertner, Aug 24 2019
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..148 (terms 1..123 from Chai Wah Wu)
factordb, Factors of n^n+1.
FORMULA
EXAMPLE
a(3) = 3: 3^3 + 1 = 28 = 2^2 * 7.
a(4) = 1: 4^4 + 1 = 257 is prime.
a(5) = 3: 5^5 + 1 = 3126 = 2 * 3 * 521.
PROG
(PARI) for(k=1, 60, print1(bigomega(k^k+1), ", ")) \\ Hugo Pfoertner, Aug 24 2019
CROSSREFS
KEYWORD
nonn,hard
AUTHOR
Jason Earls, Jul 20 2003
EXTENSIONS
More terms from Ray G. Opao, Aug 25 2004
Corrected 8 existing terms and a(46)-a(72) from Donovan Johnson, Sep 27 2010
a(73)-a(84) added by Hugo Pfoertner, Aug 24 2019
STATUS
approved