A189763 Even numbers n such that solutions to x' = n are not all semiprimes, where x' denotes the arithmetic derivative (A003415).

12, 16, 24, 32, 44, 48, 56, 60, 68, 72, 80, 92, 96, 108, 112, 120, 124, 128, 140, 152, 156, 162, 164, 168, 176, 188, 192, 212, 216, 220, 236, 240, 244, 248, 252, 272, 284, 288, 296, 316, 318, 320, 324, 332, 336, 350, 356, 360, 368, 378, 380, 384, 392, 408

Offset: 1

Author

T. D. Noe, Apr 27 2011

Keywords

• nonn

Comments

It appears that the anti-derivatives of even numbers n are overwhelmingly semiprimes of the form (n/2)^2 - k^2. For example, 1000 has 28 anti-derivatives, all semiprimes.

Crossrefs

Cf. A003415, A189762, A189764.