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40 (number)

Natural number, composite number

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Though the word is related to four (4), the spelling forty replaced fourty during the 17th century and is now the standard form.

Mathematics

40 is an abundant number.

Swiss mathematician Leonhard Euler noted 40 prime numbers generated by the quadratic polynomial n2+n+41, with values n=0,1,2,...,39. These forty prime numbers are the same prime numbers that are generated using the polynomial n2−n+41 with values of n from 1 through 40, and are also known in this context as Euler's "lucky" numbers.

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