# What Number Comes Next? Ask the Encyclopedia of Integer Sequences.

What Number Comes Next? Ask the Encyclopedia of Integer Sequences

Numbers are all around us, and they play a significant role in our daily lives. Whether we are counting the seconds until lunchtime or balancing a checkbook, numbers are essential. But what about number patterns? Have you ever noticed them in your daily routine?

Number patterns are critical in mathematics and are used to solve complex problems. They also hold an allure for anyone who enjoys puzzles or brain teasers. The question “What number comes next?” is a classic example of a number pattern puzzle that has confounded many of us at some point in our lives.

The answer to this question can often be found in a mathematical tool called the Encyclopedia of Integer Sequences (OEIS). The OEIS is an online database of over 330,000 integer sequences – patterns of numbers that follow a particular rule. The sequences are created and organized by mathematicians and enthusiasts from all over the world who contribute to the database.

But how does one use the OEIS to find the next number in a sequence? Let us consider an example to demonstrate the process.

Suppose we have the sequence of numbers: 2, 4, 6, 8, 10, 12, …

We can start by entering the first few terms of the sequence into the OEIS search engine, and it will generate a list of sequences that match the initial terms. Looking at the list. we notice that Sequence A000027 matches our sequence, and it is named the Sequence of Even Numbers.

Clicking on the name of the sequence will lead us to a page that contains a wealth of information about the sequence. The page provides the first 1000 numbers in the sequence, along with a mathematical formula that describes how to generate the sequence. In our example, the formula given is 2n, which means that each term in the sequence can be obtained by multiplying the previous term by 2.

Using the formula, we can predict the next term in the sequence quickly. Since the last term in our initial sequence was 12, the next term generated by the formula would be 2(12)= 24. Thus, the next number in the sequence is 24.

The OEIS is an invaluable tool for mathematical research and exploration, but it is also an excellent resource for anyone interested in number patterns. The database offers a vast collection of sequences to explore, ranging from simple patterns to complex mathematical concepts.

For example, Sequence A000108, known as the Catalan Numbers, pertains to a variety of natural and physical phenomena. It counts the number of ways to stack n pairs of parentheses, or the number of paths connecting two points in a grid that stay below the diagonal line. The first few numbers in the sequence are 1, 1, 2, 5, 14, 42, 132, 429, 1430, 4862, 16796, and so on.

The page dedicated to this sequence notes that it is named after the Belgian mathematician Eugene Catalan and that the sequence appears in various areas of mathematics, including combinatorics, probability theory, and algebraic geometry. It also provides a formula for calculating the nth term in the sequence, along with graphs and illustrations that help visualize the pattern.

Some sequences are more mysterious than others, and finding the next number may require more creativity and intuition than mathematical formulas. Sequence A073841, for instance, is defined as “Numbers m such that m + phi(m) is prime, where phi(m) is the Euler totient function”. The first few numbers in the sequence are 2, 5, 8, 12, 17, 20, 21, 23, 26, 27, 29, 30, 33, 35, and so on.

At first glance, this sequence may seem random and nonsensical. However, a closer look reveals a curious pattern. For example, notice that there are several pairs of consecutive numbers. 20 and 21, 26 and 27, and 33 and 35 are just a few examples. What is the significance of these pairs, if any? Do they offer any insight into the logic behind the sequence?

Questions such as these demonstrate the beauty and intrigue of number patterns. They challenge our minds and encourage us to explore beyond the familiar. And the OEIS provides a wealth of material to support this exploration.

In conclusion, the Encyclopedia of Integer Sequences is a powerful mathematical tool that unlocks the world of number patterns. It provides a gateway to a vast collection of sequences, each with its unique story and insights. By providing mathematical formulas, visualizations, and explanations, the OEIS enhances our understanding of number patterns and inspires us to explore further. It invites us to ask questions and to experience the wonder and excitement of mathematics.