A number x in which the first n decimal digits of the fractional part frac(x) sum to 666 is known as an evil number. However, the term "evil" is also used to denote nonnegative integers that have an even number of 1s in their binary expansions, the first few of which are 0, 3, 5, 6, 9, 10, 12, 15, 17, 18, 20, ... (OEIS A001969), illustrated above as a binary plot. Numbers that are not evil are then known as odious numbers. Returning to Pegg's definition of evil, the fact that π is evil was noted by Keith, while I. Honig noted that the golden ratio ϕ is also evil. The following table gives a list of some common evil numbers.

apocalypse number | beast number | economical number | happy number | lucky number | odious number | unhappy number | wasteful number