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  2. Interchangeable NPA and central office codes - Wikipedia

    en.wikipedia.org/wiki/Interchangeable_NPA_and...

    From 1947 to 1995, all NPA codes were distinguished with the digits 0 or 1 in the middle position. This provided the traditional format N 0/1 X, where N is any digit from 2 to 9, and X is any of the ten numerals. This format provided a set of 160 combinations, but only 144 were in use for geographic NPA codes.

  3. List of numeral systems - Wikipedia

    en.wikipedia.org/wiki/List_of_numeral_systems

    This is the minimum number of characters needed to encode a 32 bit number into 5 printable characters in a process similar to MIME-64 encoding, since 85 5 is only slightly bigger than 2 32. Such method is 6.7% more efficient than MIME-64 which encodes a 24 bit number into 4 printable characters.

  4. Numerical digit - Wikipedia

    en.wikipedia.org/wiki/Numerical_digit

    The total value of the number is 1 ten, 0 ones, 3 tenths, and 4 hundredths. The zero, which contributes no value to the number, indicates that the 1 is in the tens place rather than the ones place. The place value of any given digit in a numeral can be given by a simple calculation, which in itself is a complement to the logic behind numeral ...

  5. Quaternary numeral system - Wikipedia

    en.wikipedia.org/wiki/Quaternary_numeral_system

    Quaternary / k w ə ˈ t ɜːr n ər i / is a numeral system with four as its base.It uses the digits 0, 1, 2, and 3 to represent any real number.Conversion from binary is straightforward.

  6. Telephone exchange names - Wikipedia

    en.wikipedia.org/wiki/Telephone_exchange_names

    Telephone numbers listed in 1920 in New York City having three-letter exchange prefixes. In the United States, the most-populous cities, such as New York City, Philadelphia, Boston, and Chicago, initially implemented dial service with telephone numbers consisting of three letters and four digits (3L-4N) according to a system developed by W. G. Blauvelt of AT&T in 1917. [1]

  7. Binary-coded decimal - Wikipedia

    en.wikipedia.org/wiki/Binary-coded_decimal

    In this case, positive numbers always have a most significant digit between 0 and 4 (inclusive), while negative numbers are represented by the 10's complement of the corresponding positive number. As a result, this system allows for 32-bit packed BCD numbers to range from −50,000,000 to +49,999,999, and −1 is represented as 99999999.

  8. de Bruijn sequence - Wikipedia

    en.wikipedia.org/wiki/De_Bruijn_sequence

    For example, a digital door lock with a 4-digit code (each digit having 10 possibilities, from 0 to 9) would have B (10, 4) solutions, with length 10 000. Therefore, only at most 10 000 + 3 = 10 003 (as the solutions are cyclic) presses are needed to open the lock, whereas trying all codes separately would require 4 × 10 000 = 40 000 presses.

  9. 6174 - Wikipedia

    en.wikipedia.org/wiki/6174

    All other four-digit numbers eventually reach 6174 if leading zeros are used to keep the number of digits at 4. For numbers with three identical digits and a fourth digit that is one higher or lower (such as 2111), it is essential to treat 3-digit numbers with a leading zero; for example: 2111 – 1112 = 0999; 9990 – 999 = 8991; 9981 – 1899 ...