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The symbol # is known variously in English-speaking regions as the number sign, [1] hash, [2] or pound sign. [3] The symbol has historically been used for a wide range of purposes including the designation of an ordinal number and as a ligatured abbreviation for pounds avoirdupois – having been derived from the now-rare ℔ .
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.
The numero sign or numero symbol, № (also represented as Nº, No̱, №, No., or no.), [1] [2] is a typographic abbreviation of the word number(s) indicating ordinal numeration, especially in names and titles. For example, using the numero sign, the written long-form of the address "Number 29 Acacia Road" is shortened to "№ 29 Acacia Rd ...
Johann Rahn introduced the division sign (÷, an obelus variant repurposed) and the therefore sign (∴) in 1659. William Jones used π in Synopsis palmariorum mathesios [ 58 ] in 1706 because it is the initial letter of the Greek word perimetron (περιμετρον), which means perimeter in Greek.
c. 20,000 BC — Nile Valley, Ishango Bone: suggested, though disputed, as the earliest reference to prime numbers as also a common number. [1] c. 3400 BC — the Sumerians invent the first so-known numeral system, [dubious – discuss] and a system of weights and measures.
A number has a terminating or repeating expansion if and only if it is rational; this does not depend on the base. A number that terminates in one base may repeat in another (thus 0.3 10 = 0.0100110011001... 2). An irrational number stays aperiodic (with an infinite number of non-repeating digits) in all integral bases.
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1. Denotes either a plus sign or a minus sign. 2. Denotes the range of values that a measured quantity may have; for example, 10 ± 2 denotes an unknown value that lies between 8 and 12. ∓ (minus-plus sign) Used paired with ±, denotes the opposite sign; that is, + if ± is –, and – if ± is +. ÷ (division sign)