**Pronic Numbers** are numbers that are the product of two consecutive integers; 2, 6, 12, 20, 30... They are also called rectangular or **oblong numbers**. Pronic seems to be a misspelling of *promic*, from the Greek *promekes*, for rectangular, oblate or oblong. Neither pronic nor promic seems to appear in most modern dictionaries. Richard Guy pointed out to the Hyacinthos newsgroup that pronic had been used by Euler in series one, volume fifteen of his Opera, so the mathematical use of the "n" form has a long history.

**Oblong** is from the Latin *ob* (excessive) + *longus* (long). The word oblong is also commonly used as an alternate name for a rectangle. In his translation of Euclid's "Elements", Sir Thomas Heath translates the Greek word *eteromhkes*[hetero mekes - literally "different lengths"] in Book one, Definition 22 as oblong. . "Of Quadrilateral figures, a square is that which is both equilateral and right-angled; an **oblong** that which is right angled but not equilateral..."

Octave 1:2

fifth 2:3

fourth 3:4

major third 4:5 ... etc

## No comments:

Post a Comment