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magic number

noun, Physics.
1.
the atomic number or neutron number of an exceptionally stable nuclide.
Origin of magic number
1945-1950
1945-50
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the Web for magic number
Contemporary Examples
Historical Examples
  • Turning away from the curious throng, Mark cupped his hand, then together they all three peered at that magic number.

    A Ticket to Adventure Roy J. Snell
  • They then said, "We are only three Ju Ju men; you must get seven more of us, making the magic number of ten."

  • The ring becoming seven mountains suggests with its magic number an Oriental origin.

    Filipino Popular Tales Dean S. Fansler
  • Its letters make up the magic number 365, supposed to represent the number of spirits subject to the supreme being.

  • Some conjurers say that number three is the magic number, and some say number seven.

British Dictionary definitions for magic number

magic number

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
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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magic number in Science
magic number
  (māj'ĭk)   
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.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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magic number in Technology
jargon, programming
1. In source code, some non-obvious constant whose value is significant to the operation of a program and that is inserted inconspicuously in-line (hard-coded), rather than expanded in by a symbol set by a commented "#define". Magic numbers in this sense are bad style.
2. A number that encodes critical information used in an algorithm in some opaque way. The classic examples of these are the numbers used in hash or CRC functions or the coefficients in a linear congruential generator for pseudorandom numbers. This sense actually predates, and was ancestral to, the more common sense 1.
3. Special data located at the beginning of a binary data file to indicate its type to a utility. Under Unix, the system and various applications programs (especially the linker) distinguish between types of executable file by looking for a magic number. Once upon a time, these magic numbers were PDP-11 branch instructions that skipped over header data to the start of executable code; 0407, for example, was octal for "branch 16 bytes relative". Nowadays only a wizard knows the spells to create magic numbers. MS DOS executables begin with the magic string "MZ".
*The* magic number, on the other hand, is 7+/-2. The paper cited below established the number of distinct items (such as numeric digits) that humans can hold in short-term memory. Among other things, this strongly influenced the interface design of the phone system.
["The magical number seven, plus or minus two: some limits on our capacity for processing information", George Miller, in the "Psychological Review" 63:81-97, 1956].
[Jargon File]
(2003-07-02)
The Free On-line Dictionary of Computing, © Denis Howe 2010 http://foldoc.org
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10
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