A224217 Numbers b such that b^2 + 4*b + 9 is prime.

4, 10, 34, 46, 70, 76, 94, 112, 124, 160, 166, 196, 202, 244, 256, 292, 334, 340, 370, 412, 430, 454, 460, 490, 502, 514, 532, 550, 574, 586, 592, 622, 664, 712, 724, 754, 766, 784, 790, 796, 802, 832, 850, 874, 886, 916, 952, 994

Offset: 1

Author

M. F. Hasler, Apr 01 2013

Keywords

• nonn

Comments

Inspired by Sun's conjecture in A224197: Also, bases b such that the number (with digits) [1;4;9] in base b is prime.

All terms are congruent to 4 (mod 6), i.e., a(n) = 4 + 6 x(n) with x=(0, 1, 5, 7, 11, 12, 15, 18, 20, 26, 27, 32, 33, 40, 42, 48, 55, 56, 61, 68, 71, 75, 76,...)

Programs

Mathematica

Select[Range[1000],PrimeQ[#^2+4#+9]&] (* Harvey P. Dale, Sep 23 2020 *)