An abundant number is a number n for which its sum of divisors is greater than 2n. 12 is an abundant number because 1 + 2 + 3 + 4 + 6 + 12 > 24. 18 is also an abundant number because 1 + 2 + 3 + 6 + 9 + 18 > 36. The series is in the Online Encyclopedia of Integer Sequences (Sloane) as A005101. 945 is the first odd abundant number.
If a number is not abundant, it is called either deficient or perfect.