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A121068
Numbers k such that 8*k^2 + 7 is prime.
2
0, 3, 27, 30, 33, 48, 57, 60, 72, 75, 78, 108, 117, 123, 135, 150, 162, 192, 198, 207, 228, 243, 270, 300, 303, 312, 342, 345, 390, 408, 417, 423, 435, 480, 498, 507, 510, 513, 543, 552, 555, 573, 618, 633, 642, 645, 657, 675, 705, 723, 732, 738, 747, 750, 780
OFFSET
1,2
COMMENTS
All terms are multiples of 3. - Zak Seidov, Aug 11 2006
A201704 is primes of form 8*k^2+7. James C. McMahon, Oct 12 2024
EXAMPLE
If k=135 then 8*k^2 + 7 = 145807 (prime).
MAPLE
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
MATHEMATICA
Select[Range[0, 780], PrimeQ[8#^2+7]&] (* James C. McMahon, Oct 12 2024 *)
PROG
(Magma) [ n: n in [0..1500] | IsPrime(8*n^2 + 7) ]; // Vincenzo Librandi, Jan 31 2011
(PARI) is(n)=isprime(8*n^2+7) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
Sequence in context: A010257 A334567 A284863 * A136895 A319391 A034594
KEYWORD
nonn,easy
AUTHOR
Parthasarathy Nambi, Aug 10 2006
EXTENSIONS
More terms from Emeric Deutsch and Joshua Zucker, Aug 11 2006
STATUS
approved