Definitions for magic number

This page provides all possible meanings and translations of the word magic number

Princeton's WordNet

  1. magic number(noun)

    the atomic number of an extra stable strongly bound atomic nucleus: 2, 8, 20, 28, 50, 82 or 126

Wiktionary

  1. magic number(Noun)

    the number of neutrons or protons in nuclei which are required to fill the major quantum shells, and thus produce exceptionally stable nuclei - 2, 8, 20, 28, 50, 82 & 126

  2. magic number(Noun)

    A metric used to determine a team's required performance to make the playoffs.

Freebase

  1. Magic number

    In nuclear physics, a magic number is a number of nucleons such that they are arranged into complete shells within the atomic nucleus. The seven most widely recognised magic numbers as of 2007 are 2, 8, 20, 28, 50, 82, and 126. Atomic nuclei consisting of such a magic number of nucleons have a higher average binding energy per nucleon than one would expect based upon predictions such as the semi-empirical mass formula and are hence more stable against nuclear decay. The unusual stability of isotopes having magic numbers means that transuranium elements can be created with extremely large nuclei and yet not be subject to the extremely rapid radioactive decay normally associated with high atomic numbers. Large isotopes with magic numbers of nucleons are said to exist in an island of stability. Unlike the magic numbers 2–126, which are realized in spherical nuclei, theoretical calculations predict that nuclei in the island of stability are deformed. Before this was realized, higher magic numbers, such as 184 and 258, were predicted based on simple calculations that assumed spherical shapes. It is now believed that the sequence of spherical magic numbers cannot be extended in this way.

The New Hacker's Dictionary

  1. magic number

    [Unix/C; common] 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 (hardcoded), 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 pseudo-random numbers. This sense actually predates and was ancestral to the more common sense 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’. Many other kinds of files now have magic numbers somewhere; some magic numbers are, in fact, strings, like the !<arch> at the beginning of a Unix archive file or the %! leading PostScript files. Nowadays only a wizard knows the spells to create magic numbers. How do you choose a fresh magic number of your own? Simple — you pick one at random. See? It's magic! 4. An input that leads to a computational boundary condition, where algorithm behavior becomes discontinuous. Numeric overflows (particularly with signed data types) and run-time errors (divide by zero, stack overflows) are indications of magic numbers. The Y2K scare was probably the most notorious magic number non-incident.The magic number, on the other hand, is 7±2. See The magical number seven, plus or minus two: some limits on our capacity for processing information by George Miller, in the Psychological Review 63:81-97 (1956). This classic paper 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.

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"magic number." Definitions.net. STANDS4 LLC, 2014. Web. 22 Aug. 2014. <http://www.definitions.net/definition/magic number>.

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