A121068 - OEIS

%I #22 Oct 12 2024 21:32:25

%S 0,3,27,30,33,48,57,60,72,75,78,108,117,123,135,150,162,192,198,207,

%T 228,243,270,300,303,312,342,345,390,408,417,423,435,480,498,507,510,

%U 513,543,552,555,573,618,633,642,645,657,675,705,723,732,738,747,750,780

%N Numbers k such that 8*k^2 + 7 is prime.

%C All terms are multiples of 3. - _Zak Seidov_, Aug 11 2006

%C A201704 is primes of form 8*k^2+7. _James C. McMahon_, Oct 12 2024

%e If k=135 then 8*k^2 + 7 = 145807 (prime).

%p a:=proc(n) if isprime(8*n^2+7)=true then n else fi end: seq(a(n),n=0..1000); # _Emeric Deutsch_, Aug 11 2006

%t Select[Range[0,780],PrimeQ[8#^2+7]&] (* _James C. McMahon_, Oct 12 2024 *)

%o (Magma) [ n: n in [0..1500] | IsPrime(8*n^2 + 7) ]; // _Vincenzo Librandi_, Jan 31 2011

%o (PARI) is(n)=isprime(8*n^2+7) \\ _Charles R Greathouse IV_, Jun 13 2017

%Y Cf. A007522, A201704.

%K nonn,easy,changed

%O 1,2

%A _Parthasarathy Nambi_, Aug 10 2006

%E More terms from _Emeric Deutsch_ and _Joshua Zucker_, Aug 11 2006