A121068 Numbers k such that 8*k^2 + 7 is prime.

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

Links

Table of n, a(n) for n=1..55.

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

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

Cf. A007522.

Sequence in context: A010257 A334567 A284863 * A136895 A319391 A034594

Adjacent sequences: A121065 A121066 A121067 * A121069 A121070 A121071

Keyword

nonn,easy

Author

Parthasarathy Nambi, Aug 10 2006

Extensions

More terms from Emeric Deutsch and Joshua Zucker, Aug 11 2006

Status

approved