Given two natural numbers and with , let be the set which contains all natural numbers not greater than N and not divisible by any number between and (inclusive). For example,
4 can divide 4 and 8
5 can divide 5 and 10
6 can divide 6
Hence 4,5,6,8 and 10 will not appear in the set which represents. Although they are all not greater than 10.
We define the product of a set as the product of all elements in that set, written as P({...}) where {...} is a specific set. For example,
Finally, We define a function as the sum of product of sets over all 's subsets which contain exactly K elements.