The definition of a pernicious number:

In number theory, a pernicious number is a positive integer where the Hamming weight (or digit sum) of its binary representation is prime.

The meaning of 'pernicious':

pernicious (adj.) : highly injurious or destructive, deadly

Intriguing. How did pernicious numbers end up being called that?

odiousif $t(n)$ is odd andevilif $t(n)$ is even. Thus every number is either odious or evil, and therefore the words "odious" and "evil" cannot be pejorative in this context. It seems very likely that "pernicious" was chosen in the same spirit because it starts with the letter "p". $\endgroup$ – Steven Landsburg Jan 24 '15 at 11:42