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pronic number

Also known as a rectangular or oblong number, a number that is the product of two consecutive integers: 2 (1 × 2), 6 (2 × 3), 12 (3 × 4), 20 (4 × 5), ... The pronic numbers are twice the triangular numbers, and represent the lengths that produce the musical intervals: octave (1:2), fifth (2:3), fourth (3:4), major third (4:5) .... Pronic seems to be a misspelling of promic, from the Greek promekes, for rectangular or oblong; however, the "n" form goes back at least far as Leonhard Euler who used it in series one, volume fifteen of his Opera.

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