Six is the first 'Perfect Number', i.e. a number that is the sum of all of its factors (excluding itself), which is the second?
Abundant number "s"("n")-"n"). The first 28 abundant numbers are: For example, the proper divisors of 24 are 1, 2, 3, 4, 6, 8, and 12, whose sum is 36. Because 36 is more than 24, the number 24 is abundant. Its abundance is 36 − 24 = 12. Numbers whose sum of proper factors equals the number itself (such as 6 and 28) are called perfect numbers, while numbers whose sum of proper factors is less than the number itself are called deficient numbers. The first known classification of numbers as deficient, perfect or abundant was by Nicomachus in his "Introductio Arithmetica"
Perfect number number. Most abundant numbers are also semiperfect; abundant numbers which are not semiperfect are called weird numbers. Perfect number In number theory, a perfect number is a positive integer that is equal to the sum of its proper positive divisors, that is, the sum of its positive divisors excluding the number itself (also known as its aliquot sum). Equivalently, a perfect number is a number that is half the sum of all of its positive divisors (including itself) i.e. "σ"("n") = 2"n". This definition is ancient, appearing as early as Euclid's Elements (VII.22) where it is called ("perfect", "ideal", or