Sequences and Patterns – Mathigon (2024)

Many professions that use mathematics are interested in one specific aspect – finding patterns, and being able to predict the future. Here are two examples:

Geologists around the world want to predict earthquakes and volcano eruptions. They can try to find patterns in historical data of from seismographs, of the atmosphere, or even animal behaviour. One earthquake, for example, might trigger aftershocks later.

Bankers also look at historical data of stock prices, interest rates and currency exchange rates to estimate how financial markets might change in the future. Being able to predict if the value of a stock will go up or down can be extremely lucrative!

Professional mathematicians use highly complex algorithms to find and analyse all these patterns, but for now, let’s start with something much simpler.

Simple Sequences

In mathematics, a sequence is a chain of numbers (or other objects) that usually follow a particular pattern. The individual elements in a sequence are called terms.

Here are a few examples of sequences. Can you find their patterns and calculate the next two terms?

3, 6 +3, 9 , 12 , 15 , , … Pattern: “Add 3 to the previous number to get the next one.”

4, 10 , 16 , 22 , 28 , , , … Pattern: “Add 6 to the previous number to get the next one.”

3, 4 , 7 , 8 , 11 , , , … Pattern: “Alternatingly add 1 and add 3 to the previous number, to get the next one.”

1, 2 , 4 , 8 , 16 , , , … Pattern: “Multiply the previous number by 2, to get the next one.”

The dots (…) at the end simply mean that the sequence can go on forever. When referring to sequences like this in mathematics, we often represent every term by a special variable:

x1,x2,x3,x4,x5,x6,x7,

The small number after the x is called a subscript, and indicates the position of the term in the sequence. This means that we can represent the nth term in the sequence by .

Triangle and Square Numbers

Sequences in mathematics don’t always have to be numbers. Here is a sequence that consists of geometric shapes – triangles of increasing size:

1

3

6

At every step, we’re adding one more row to the previous triangle. The length of these new rows also increases by one every time. Can you see the pattern?

1, 3 +2, 6 +3, 10 +4, 15 +5, 21 +6 +7, +8, …

We can also describe this pattern using a special formula:

xn=xn1+n

To get the n-th triangle number, we take the triangle number and add n. For example, if n=${n}, the formula becomes x${n}=x${n-1}+${n}.

A formula that expresses xn as a function of previous terms in the sequence is called a recursive formula. As long as you know the in the sequence, you can calculate all the following ones.

Another sequence which consists of geometric shapes are the square numbers. Every term is formed by increasingly large squares:

1

4

9

For the triangle numbers we found a recursive formula that tells you the next term of the sequence as a function of of its previous terms. For square numbers we can do even better: a formula that tells you the nth term directly, without first having to calculate all the previous ones:

xn =

This is called an explicit formula. We can use it, for example, to calculate that the 13th square number is , without first finding the previous 12 square numbers.

Let’s summarise all the definitions we have seen so far:

A sequence is a list of numbers, geometric shapes or other objects, that follow a specific pattern. The individual items in the sequence are called terms, and represented by variables like xn.

A recursive formula for a sequence tells you the value of the nth term as a function of . You also have to specify the first term(s).

An explicit formula for a sequence tells you the value of the nth term as a function of , without referring to other terms in the sequence.

Action Sequence Photography

In the following sections you will learn about many different mathematical sequences, surprising patterns, and unexpected applications.

First, though, let’s look at something completely different: action sequence photography. A photographer takes many shots in quick succession, and then merges them into a single image:

Can you see how the skier forms a sequence? The pattern is not addition or multiplication, but a geometric transformation. Between consecutive steps, the skier is both translated and .

Here are a few more examples of action sequence photography for your enjoyment:

Sequences and Patterns – Mathigon (2024)

FAQs

What is the sequence of 2, 5, 8, 11? ›

2, 5, 8, 11, 14, 17, 20, 23, 26, 29, 32, ..

What is the pattern of 2,6,10,14? ›

A sequence with general term an+1=an+d is called an arithmetic sequence, an=nth term and d=common difference. The general (nth) term for 2, 6, 10, 14, 18, 22, … is 4 and the first term is 2. If we let d=4 this becomes an=a1+(n−1)d. The nth or general term of an arithmetic sequence is given by an=a1+(n−1)d.

What are the 5 patterns in math? ›

There are different types of patterns in mathematics, such as number patterns, image patterns, logic patterns, word patterns, and so on. The number pattern is the most commonly used one since students are aware of even numbers, odd numbers, skip counting, etc., which help in understanding these patterns easily.

What is the sequence formula? ›

The formula for the nth term in an arithmetic sequence is an=a1+(n−1)d. This formula can be used to determine the value of any term in an arithmetic sequence. An arithmetic sequence has a common difference between every term.

What is a pattern rule in math? ›

Pattern Rules. A numerical pattern is a sequence of numbers that has been created based on a formula or rule called a pattern rule. Pattern rules can use one or more mathematical operations to describe the relationship between consecutive numbers in the pattern. There are two primary categories of numerical patterns.

How can I calculate sequence? ›

To find the nth term of a sequence use the formula an=a1+(n−1)d. Here's how to understand this nth term formula. To find the nth term, first calculate the common difference, d . Next multiply each term number of the sequence (n = 1, 2, 3, …) by the common difference.

Why is 5 the 100th number? ›

100 - 9 = 91. Count the next 45 numbers and you will have reached the 99th digit. 9 + 45 = 54. the 100th digit is 5.

What is the n-th term? ›

The 𝒏th term refers to a term's position in the sequence, for example, the first term has 𝒏 = 1, the second term has 𝒏 = 2 and so on. An expression for the 𝒏th term is worked out by looking at the difference between the terms of the sequence and comparing the sequence to the appropriate times table.

Is 2 6 10 14 a geometric sequence? ›

This is an arithmetic sequence since there is a common difference between each term. In this case, adding 4 to the previous term in the sequence gives the next term.

What are the next three numbers in this pattern 1 2 4 7 11 ___ ___ ___? ›

1, 2, 4, 7, 11, 16, 22, 29, 37, 46, 56, 67, 79, 92, 106, 121, 137, 154, 172, 191, 211, ... Its three-dimensional analogue is known as the cake numbers. The difference between successive cake numbers gives the lazy caterer's sequence.

What number is needed to complete the pattern 66 73 13 21 52 10 20? ›

Summary: The number needed to complete the pattern 66 73 13 21 52 __ 10 20 is 61.

What is the formula for finding patterns? ›

A linear number pattern is a list of numbers in which the difference between each number in the list is the same. The formula for the nth term of a linear number pattern, denoted an, is an = dn - c, where d is the common difference in the linear pattern and c is a constant number.

What is the formula for finding the sequence? ›

To find the nth term of a sequence use the formula an=a1+(n−1)d. Here's how to understand this nth term formula. To find the nth term, first calculate the common difference, d . Next multiply each term number of the sequence (n = 1, 2, 3, …) by the common difference.

How do you solve figure patterns? ›

If two or more terms in the sequence are given, we can use addition or subtraction to find the arithmetic pattern. For example, 2, 4, 6, 8, 10, __, 14, __. Now, we need to find the missing term in the sequence. Here, we can use the addition process to figure out the missing terms in the patterns.

References

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