mathematics

73 (number)

73 (number) is a mathematics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand 73 (number) rather than just read about it. In short: 73 (seventy-three) is the natural number following 72 and preceding 74. It is a prime number.

Key takeaways

73 (number) belongs to mathematics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect 73 (number) to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of 73 (number) from memory before moving on to harder problems.

Reference excerpt

73 (seventy-three) is the natural number following 72 and preceding 74. It is a prime number.

In mathematics 73 is a prime number, a twin prime (with 71), a Pierpont prime, and a star number.

Sheldon prime 73 is the unique Sheldon prime, named as an homage to TV character Sheldon Cooper. Where 73 and 37 are part of the sequence of permutable primes and emirps in base-ten, a Sheldon prime as defined as satisfying "mirror" and "product" properties, where:

73 has 37 as the mirroring of its decimal digits. 73 is the 21st prime number, and 37 the 12th. The "mirror property" is fulfilled when 73 has a mirrored permutation of its digits (37) that remains prime. Similarly, their respective prime indices (21 and 12) in the list of prime numbers are also permutations of the same digits (1, and 2). 73 is the 21st prime number. It satisfies the "product property" since the product of its decimal digits is precisely in equivalence with its index in the sequence of prime numbers. i.e., 21 = 7 × 3. On the other hand, 37 does not fulfill the product property, since, naturally, its digits also multiply to 21; therefore, the only number to fulfill this property between these two numbers is 73, and as such it is the only "Sheldon prime".

In other fields 73 is also:

Amateur radio operators and other morse code users commonly use the number 73 as a "92 Code" abbreviation for "best regards", typically when ending a QSO (a conversation with another operator). These codes also facilitate communication between operators who may not be native English speakers. In Morse code, 73 is an easily recognized palindrome: ( - - · · · · · · - - ). On a CB radio, 10-73 means "speed trap at..."

Popular culture

The Big Bang Theory 73 is Sheldon Cooper's favorite number in the television series The Big Bang Theory. He first expresses his love for it in episode 73, "The Alien Parasite Hypothesis" (2010). Jim Parsons, who plays Cooper in the series, was born in 1973. His character often wears a t-shirt with the number 73 on it.

Worked examples

Example 1 — a first encounter with 73 (number)

Start with the simplest possible case. Write down what 73 (number) claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In mathematics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to 73 (number) before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about 73 (number) ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of 73 (number)

In research: 73 (number) appears in mathematics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses 73 (number) in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: 73 (number) is common in secondary-school and first-year university syllabi. It links to neighbouring topics Integers, Numbers, Prime numbers, so understanding it makes those chapters shorter.
In everyday life: Look for 73 (number) outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study 73 (number) in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what 73 (number) means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain 73 (number) out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is 73 (number) in simple terms?

73 (seventy-three) is the natural number following 72 and preceding 74. It is a prime number.

Why does 73 (number) matter?

Because it connects several mathematics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study 73 (number)?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on 73 (number).