magic number

American  

noun

Physics.

1. the atomic number or neutron number of an exceptionally stable nuclide.

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magic number British  

noun

1. physics any of the numbers 2, 8, 20, 28, 50, 82, and 126. Nuclides with these numbers of nucleons appear to have greater stability than other nuclides

2. chem a number of atoms that is particularly stable in certain types of compound that have clusters of the same type of atom

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magic number Scientific  

/ măj′ĭk /

1. Any of the numbers, 2, 8, 20, 28, 50, 82, or 126, that represent the number of neutrons or protons in strongly bound and exceptionally stable atomic nuclei. The existence of such stable nuclei is explained by assuming a shell structure for nucleons, much like the shell structure of electron orbitals around the nucleus.

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Etymology

Origin of magic number

First recorded in 1945–50

Example Sentences

"But with so much at stake and shareholders to appease, it seems ultimately the magic number couldn't be found, at least not right now," she added.

From Barron's • Feb. 5, 2026

The magic number: For Bierbaum, $20 is the magic number, a price where customers don’t think twice when they buy.

From The Wall Street Journal • Dec. 6, 2025

After ending their embarrassing Test losing streak at 18 in Japan last summer, 12 is the magic number for Wales when they host the Brave Blossoms in Cardiff.

From BBC • Nov. 14, 2025

Read: Amazon’s stock comeback hinges on AWS hitting this magic number.

From MarketWatch • Oct. 20, 2025

Even today, a critical threshold in human organisations falls somewhere around this magic number.

From "Sapiens: A Brief History of Humankind" by Yuval Noah Harari

Related Words

• code
• confidential information
• key
• mystery