Article ID: CBB215002916

Dicuil (9th Century) on Triangular and Square Numbers (2019)

unapi

Dicuil was a ninth-century Irish monk who taught at the Carolingian school of Louis the Pious. He wrote a Computus or astronomical treatise in Latin in about 814–16, which contains a chapter on triangular and square numbers. Dicuil describes two methods for calculating triangular numbers: the simple method of summing the natural numbers, and the more complex method of multiplication, equivalent to the formula n(n + 1)/2. He also states that a square number is equal to twice a triangular number minus the generating number, equivalent to n2 = 2[n(n + 1)/2] – n. The multiplication formula for triangular numbers was first explicitly described in about the third century AD by the Greek authors Diophantus and Iamblichus. It was also known as a solution to other mathematical problems as early as 300 BC. It reappeared in the West in the sixteenth century. Dicuil thus fills a gap in our medieval knowledge.

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Authors & Contributors
Stevens, Wesley M.
Hachaichi, Yassine
Hamouda, Leïla
Manolova, Divna
Sammarchi, Eleonora
Bertolini, Manuel
Concepts
Mathematics
Arithmetic
Numbers
Manuscripts
Arab/Islamic world, civilization and culture
Geometry
Time Periods
Medieval
Early modern
Renaissance
Ancient
17th century
16th century
Places
Europe
Mediterranean region
Byzantium
Russia
Italy
France
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