A242333 Numbers k such that k^2 + 5 is a semiprime.

1, 2, 3, 4, 8, 9, 14, 18, 21, 22, 24, 26, 27, 28, 30, 33, 42, 44, 51, 54, 57, 58, 62, 63, 64, 68, 69, 82, 84, 86, 90, 93, 98, 99, 102, 104, 108, 111, 118, 132, 134, 138, 144, 152, 154, 156, 166, 174, 177, 180, 183, 184, 186, 188, 189, 194, 208, 210, 212, 216

Offset: 1

Author

Vincenzo Librandi, May 14 2014

Keywords

• nonn
• easy

Comments

The semiprimes of this form are: 6, 9, 14, 21, 69, 86, 201, 329, 446, 489, 581, 681, 734, 789, 905, 1094, 1769, 1941, 2606, 2921, 3254, ...

Links

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

Crossrefs

Cf. A056905, A078402, A085722, A242330, A242331, A242332.

Programs

Magma

IsSemiprime:=func; [n: n in [0..300] | IsSemiprime(s) where s is n^2+5];

Mathematica

Select[Range[0, 300], PrimeOmega[#^2 + 5] == 2 &]