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  2. 1/2 + 1/4 + 1/8 + 1/16 + ⋯ - Wikipedia

    en.wikipedia.org/wiki/1/2_%2B_1/4_%2B_1/8_%2B_1/...

    The geometric series on the real line. In mathematics, the infinite series 1 2 + 1 4 + 1 8 + 1 16 + ··· is an elementary example of a geometric series that converges absolutely. The sum of the series is 1. In summation notation, this may be expressed as. The series is related to philosophical questions considered in antiquity, particularly ...

  3. List of regions and sub-regions of Portugal - Wikipedia

    en.wikipedia.org/wiki/List_of_regions_and_sub...

    Administrative divisions of continental Portugal, including districts, NUTS and historical provinces. This is the list of the municipalities of Portugal under the NUTS 2 and NUTS 3 format. The NUTS 3 regions were revised in 2015; since then, the subregions (NUTS 3) coincide with the intermunicipal communities . [1]

  4. 1/4 + 1/16 + 1/64 + 1/256 + ⋯ - Wikipedia

    en.wikipedia.org/wiki/1/4_%2B_1/16_%2B_1/64_%2B...

    1/4 + 1/16 + 1/64 + 1/256 + ⋯. Archimedes' figure with a = 3 4. In mathematics, the infinite series 1 4 + 1 16 + 1 64 + 1 256 + ⋯ is an example of one of the first infinite series to be summed in the history of mathematics; it was used by Archimedes circa 250–200 BC. [1] As it is a geometric series with first term 1 4 and common ratio 1 4 ...

  5. ISO 3166-1 - Wikipedia

    en.wikipedia.org/wiki/ISO_3166-1

    ISO 3166-1. ISO 3166-1 ( Codes for the representation of names of countries and their subdivisions – Part 1: Country codes) is a standard defining codes for the names of countries, dependent territories, and special areas of geographical interest. It is the first part of the ISO 3166 standard published by the International Organization for ...

  6. Portugal - Wikipedia

    en.wikipedia.org/wiki/Portugal

    The same study found that 1.4 million people, (13% of the population), have immigration background, in which 947,500 are first generation immigrants, concentrated mainly in the Lisbon metropolitan area and the Algarve. It is noteworthy that the survey was only carried out amongst people living legally in the country for at least one year at the ...

  7. 1,1,2,2-Tetrachloroethane - Wikipedia

    en.wikipedia.org/wiki/1,1,2,2-Tetrachloroethane

    Appearance. 1,1,2,2-tetrachloroethane ( TeCA ), also known by the brand names Bonoform, Cellon and Westron, is an organic compound. It is colorless liquid and has a sweet odor. It is used as an industrial solvent and as a separation agent. TeCA is toxic and it can be inhaled, consumed or absorbed through the skin.

  8. One half - Wikipedia

    en.wikipedia.org/wiki/One_half

    One half is a rational number that lies midway between nil and unity (which are the elementary additive and multiplicative identities) as the quotient of the first two non-zero integers, . It has two different decimal representations in base ten, the familiar and the recurring , with a similar pair of expansions in any even base; while in odd ...

  9. Power of two - Wikipedia

    en.wikipedia.org/wiki/Power_of_two

    Every power of 2 (excluding 1) can be written as the sum of four square numbers in 24 ways. The powers of 2 are the natural numbers greater than 1 that can be written as the sum of four square numbers in the fewest ways. As a real polynomial, an + bn is irreducible, if and only if n is a power of two.