OFFSET
1,1
COMMENTS
First seven numbers of the form 10 * n^2 + 7 are prime numbers. They are called Trotter primes by Terrel Trotter Jr. There are 735 Trotter primes less than 10^8.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..5000
T. Trotter, Trotter numbers and Trotter primes [Warning: As of March 2018 this site appears to have been hacked. Proceed with great caution. The original content should be retrieved from the Wayback machine and added here. - N. J. A. Sloane, Mar 29 2018]
MATHEMATICA
Select[Table[10n^2+7, {n, 0, 500}], PrimeQ] (* Vincenzo Librandi, Dec 04 2011 *)
Select[(10*Range[0, 70]^2+7), PrimeQ] (* Harvey P. Dale, Dec 11 2018 *)
PROG
(Magma) [a: n in [0..300] | IsPrime(a) where a is 10*n^2+7]; // Vincenzo Librandi, Dec 05 2011
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Kausthub Gudipati, Sep 25 2011
EXTENSIONS
7 inserted by Omar E. Pol, Oct 03 2011
Restored the primitive offset by Vincenzo Librandi, Dec 04 2011
STATUS
approved