OFFSET
1,1
COMMENTS
Numbers k > 1 such that k^2 + k + 1 is a prime. - Vincenzo Librandi, Nov 16 2010
Therefore essentially the same as A002384. - Georg Fischer, Oct 06 2018
LINKS
Hugo Pfoertner, Table of n, a(n) for n = 1..10000
EXAMPLE
a(5) = 8 because (8^3-1)/(8-1) = 511/7 = 73 is prime.
MATHEMATICA
Select[Range[2, 550], PrimeQ[(#^3-1)/(#-1)]&] (* Harvey P. Dale, Sep 10 2009 *)
PROG
(PARI) is(n)=isprime(n^2+n+1) \\ Charles R Greathouse IV, Jun 05 2017
(Magma) [n: n in [2..220] |IsPrime((n^3-1) div (n -1))]; // Vincenzo Librandi, Oct 07 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Hugo Pfoertner, Jun 22 2004
EXTENSIONS
3 and 5 added by Daniel McCandless (dkmccandless(AT)gmail.com), Aug 31 2009
Corrected terms, including many previously omitted terms, from Harvey P. Dale, Sep 10 2009
STATUS
approved