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In combinatorial mathematics, the Bell numbers count the possible partitions of a set. These numbers have been studied by mathematicians since the 19th century, and their roots go back to medieval Japan. In an example of Stigler's law of eponymy, they are named after Eric Temple Bell, who wrote about them in the 1930s.
Kenmore 9392 is a five-pull (1L-4N) small-city telephone number for the Kenmore exchange in Fort Wayne, Indiana. MArket 7032 is a six-digit (2L-4N) telephone number. This format was in use from the 1920s through the 1950s, and was phased out c. 1960. BALdwin 6828 is an urban 3L-4N example, used only in the largest cities before conversion to ...
The ordered Bell numbers were studied in the 19th century by Arthur Cayleyand William Allen Whitworth. They are named after Eric Temple Bell, who wrote about the Bell numbers, which count the partitions of a set; the ordered Bell numbers count partitions that have been equipped with a total order.
List of dialing codes. The North American Numbering Plan (NANP) is a telephone numbering plan for twenty-five regions in twenty countries, primarily in North America and the Caribbean. This group is historically known as World Zone 1 and has the telephone country code 1. Some North American countries, most notably Mexico, do not participate ...
Canadian (and other North American Numbering Plan) telephone numbers are usually written as (NPA) NXX-XXXX. For example, 250 555 0199, a fictional number, could be written as (250) 555-0199, 250-555-0199, 250-5550199, or 250/555-0199. The Government of Canada's Translation Bureau recommends using hyphens between groups; e.g. 250-555-0199. [4]
Toll-free telephone numbers in the North American Numbering Plan. Toll-free telephone numbers in the North American Numbering Plan have the area code prefix 800, 833, 844, 855, 866, 877, and 888. Additionally, area codes 822, 880 through 887, and 889 are reserved for toll-free use in the future. 811 is excluded because it is a special dialing ...
A telephone keypad using the ITU E.161 standard. A telephone keypad is a keypad installed on a push-button telephone or similar telecommunication device for dialing a telephone number. It was standardized when the dual-tone multi-frequency signaling (DTMF) system was developed in the Bell System in the United States in the 1960s – this ...
The railway block signalling bell code is a system of bell sounds used in Great Britain to communicate between manually operated Signal Boxes in implementing the railway block system. (The bell system is not used in modern power signal boxes, other than to any older adjacent signalboxes.) Each such signal box has a bell circuit to the boxes on ...