(mathematics) Any number in a Fibonacci sequence (being the sum of the preceding two numbers)

(mathematics) A number that represents the number of items in a pyramid having a given number of sides and layers

(physics) A quantum number related to the difference between the number of leptons and antileptons in a system

(mathematics) Any positive integer having the property that all smaller integers can be represented as sums of distinct divisors of it

plural of non-member

(mathematics) Any integer that is the sum of n natural numbers from 1 to n.

(idiomatic) Used to apologize for a possibly impolite statement one is making.

Walpurgisnacht ("Walpurga's night"), a feast of witchcraft in German folklore, observed on 30 April. / (by extension) Any orgiastic or bacchanalian party.

(mathematics, number theory) A number equal to the number of dots in a geometric figure formed of dots. The series begins with unity and is formed so that subtracting each from the following, and treating the series so formed in the same way, by a continuation of the process, yields equal differences.

Alternative form of noncontact