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  2. Primitive abundant number - Wikipedia

    en.wikipedia.org/wiki/Primitive_abundant_number

    For example, 20 is a primitive abundant number because: The sum of its proper divisors is 1 + 2 + 4 + 5 + 10 = 22, so 20 is an abundant number. The sums of the proper divisors of 1, 2, 4, 5 and 10 are 0, 1, 3, 1 and 8 respectively, so each of these numbers is a deficient number. The first few primitive abundant numbers are:

  3. History of ancient numeral systems - Wikipedia

    en.wikipedia.org/wiki/History_of_ancient_numeral...

    Number systems have progressed from the use of fingers and tally marks, perhaps more than 40,000 years ago, to the use of sets of glyphs able to represent any conceivable number efficiently. The earliest known unambiguous notations for numbers emerged in Mesopotamia about 5000 or 6000 years ago.

  4. List of numeral systems - Wikipedia

    en.wikipedia.org/wiki/List_of_numeral_systems

    A form of unary notation called Church encoding is used to represent numbers within lambda calculus. Some email spam filters tag messages with a number of asterisks in an e-mail header such as X-Spam-Bar or X-SPAM-LEVEL. The larger the number, the more likely the email is considered spam. 10: Bijective base-10: To avoid zero: 26: Bijective base-26

  5. Alphabetic numeral system - Wikipedia

    en.wikipedia.org/wiki/Alphabetic_numeral_system

    The Greek alphabet has 24 letters; three additional letters had to be incorporated in order to reach 900. Unlike the Greek, the Hebrew alphabet's 22 letters allowed for numerical expression up to 400. The Arabic abjad's 28 consonant signs could represent numbers up to 1000. Ancient Aramaic alphabets had enough letters to reach up to 9000.

  6. Letter frequency - Wikipedia

    en.wikipedia.org/wiki/Letter_frequency

    Letter frequency is the number of times letters of the alphabet appear on average in written language. Letter frequency analysis dates back to the Arab mathematician Al-Kindi (c. AD 801–873), who formally developed the method to break ciphers .

  7. Vigesimal - Wikipedia

    en.wikipedia.org/wiki/Vigesimal

    In a vigesimal place system, twenty individual numerals (or digit symbols) are used, ten more than in the decimal system. One modern method of finding the extra needed symbols is to write ten as the letter A, or A 20, where the 20 means base 20, to write nineteen as J 20, and the numbers between with the corresponding letters of the alphabet.

  8. 20 (number) - Wikipedia

    en.wikipedia.org/wiki/20_(number)

    It is the smallest primitive abundant number, [5] and the first number to have an abundance of 2, followed by 104. [6] 20 is the length of a side of the fifth smallest right triangle that forms a primitive Pythagorean triple (20, 21, 29). [7] [a] It is the third tetrahedral number. [8]

  9. Gödel numbering - Wikipedia

    en.wikipedia.org/wiki/Gödel_numbering

    The numbers involved might be very large indeed, but this is not a barrier; all that matters is that such numbers can be constructed. In simple terms, Gödel devised a method by which every formula or statement that can be formulated in the system gets a unique number, in such a way that formulas and Gödel numbers can be mechanically converted ...