OFFSET
1,1
COMMENTS
Numbers k such that k-1, k+1 and k^2+k+1 are all primes.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..5000 from Michael De Vlieger)
EXAMPLE
For k = 6: 5, 7 and 43 are prime values of the first 3 cyclotomic polynomials.
MATHEMATICA
psQ[n_]:=And@@PrimeQ[{n-1, n+1, n^2+n+1}]; Select[Range[11000], psQ] (* Harvey P. Dale, Nov 05 2011 *)
Select[Range[10500], AllTrue[Cyclotomic[Range@ 3, #], PrimeQ] &] (* Michael De Vlieger, Dec 08 2018 *)
PROG
(PARI) is(k) = isprime(k-1) && isprime(k+1) && isprime(k^2+k+1); \\ Amiram Eldar, Sep 24 2024
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Labos Elemer, May 07 2002
STATUS
approved