Select from {un} those terms whose subscripts are n1,n2,…,nk,… Then the sequence {unk} so selected (with k th term equal to \(...Select from {un} those terms whose subscripts are n1,n2,…,nk,… Then the sequence {unk} so selected (with k th term equal to unk), is called the subsequence of {un}, determined by the subscripts nk,k=1,2,3,….
The title of this section, “Counting,” is not intended to evoke the usual process of counting sheep, or counting change. What we want is to be able to count some collection in principle so that we wil...The title of this section, “Counting,” is not intended to evoke the usual process of counting sheep, or counting change. What we want is to be able to count some collection in principle so that we will be able to discover a formula for its size. There are two principles that will be indispensable in counting things: the “multiplication rule” which tells us when we should multiply, and the “addition rule” which tells us when we should add.