noun: (number theory) Any number belonging to the integer sequence whose nth element is the product of the first n primes.
noun: (number theory) A unary operation, denoted by the postfix symbol # and defined on the nonnegative integers, which maps 0 to 1, 1 to 1, and each subsequent number to the product of all primes less than or equal to it; the value mapped to by said operation for a given input.
