A242331 Numbers k such that k^2 + 3 is a semiprime.

1, 6, 16, 18, 20, 24, 26, 32, 34, 36, 40, 44, 46, 48, 56, 60, 66, 68, 78, 80, 88, 98, 100, 102, 104, 108, 116, 118, 120, 128, 136, 148, 152, 164, 170, 174, 176, 182, 188, 190, 192, 196, 200, 204, 212, 220, 226, 232, 234, 238, 246, 250, 252, 258, 260, 262, 266

Offset: 1

Author

Vincenzo Librandi, May 14 2014

Keywords

• nonn
• easy

Comments

The semiprimes of this form are: 4, 39, 259, 327, 403, 579, 679, 1027, 1159, 1299, 1603, 1939, 2119, 2307, 3139, 3603, 4359, 4627, ...

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A049422, A049423, A085722, A242330, A242332, A242333.

Programs

Magma

IsSemiprime:=func; [n: n in [0..300] | IsSemiprime(s) where s is n^2+3];

Mathematica

Select[Range[300], PrimeOmega[#^2 + 3] == 2 &]