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For example, the sequence 2, 6, 18, 54, ... is a geometric progression with a common ratio of 3. Similarly 10, 5, 2.5, 1.25, ... is a geometric sequence with a common ratio of 1/2. Examples of a geometric sequence are powers r k of a fixed non-zero number r, such as 2 k and 3 k. The general form of a geometric sequence is
The geometric series is an infinite series derived from a special type of sequence called a geometric progression.This means that it is the sum of infinitely many terms of geometric progression: starting from the initial term , and the next one being the initial term multiplied by a constant number known as the common ratio .
This formula can be motivated from the combinatorial definition and thus serves as a natural starting point for the theory. For small values of n {\textstyle n} and k {\textstyle k} , the values of A ( n , k ) {\textstyle A(n,k)} can be calculated by hand.
Two other formulas regarding triangular numbers are + = + + and = +, both of which can easily be established either by looking at dot patterns (see above) or with some simple algebra. In 1796, Gauss discovered that every positive integer is representable as a sum of three triangular numbers (possibly including T 0 = 0), writing in his diary his ...
All these sequences may be viewed as generalizations of the Fibonacci sequence. In particular, Binet's formula may be generalized to any sequence that is a solution of a homogeneous linear difference equation with constant coefficients. Some specific examples that are close, in some sense, to the Fibonacci sequence include:
An arithmetico-geometric series is a sum of terms that are the elements of an arithmetico-geometric sequence. Arithmetico-geometric sequences and series arise in various applications, such as the computation of expected values in probability theory, especially in Bernoulli processes. For instance, the sequence
The evaluation of incomplete exponential Bell polynomial B n,k (x 1,x 2,...) on the sequence of ones equals a Stirling number of the second kind: {} =, (,, …,). Another explicit formula given in the NIST Handbook of Mathematical Functions is
Proof without words of the arithmetic progression formulas using a rotated copy of the blocks. An arithmetic progression or arithmetic sequence is a sequence of numbers such that the difference from any succeeding term to its preceding term remains constant throughout the sequence. The constant difference is called common difference of that ...