A086285 Numbers k such that 1 + 2k + 3k^2 is prime.

2, 12, 14, 18, 24, 26, 32, 38, 44, 56, 62, 68, 90, 92, 98, 114, 120, 126, 128, 144, 150, 158, 164, 168, 170, 176, 180, 186, 192, 200, 210, 212, 216, 230, 246, 254, 260, 266, 276, 278, 282, 290, 300, 318, 332, 344, 354, 362, 366, 378, 396, 398, 408, 420, 432

Offset: 1

Author

Zak Seidov, Aug 28 2003

Keywords

• easy
• nonn

Comments

Excluding a(1), these are also the bases in which 321 represents a prime number.

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A056109 (3n^2+2n+1).

Programs

Mathematica

Select[Range[500],PrimeQ[1+2#+3#^2]&] (* Harvey P. Dale, Jun 23 2012 *)

PARI

is(n)=isprime(1+2*n+3*n^2) \\ Charles R Greathouse IV, Feb 17 2017