Henri–Auguste Delannoy (; 28 September 1833 – 5 February 1915) was a French army officer and amateur mathematician, after whom the

Delannoy number In mathematics, a Delannoy number D counts the paths from the southwest corner (0, 0) of a rectangular grid to the northeast corner (''m'', ''n''), using only single steps north, northeast, or east. The Delannoy numbers are named after French army ...

s are named... Delannoy grew up in

Guéret Guéret (; Occitan: ''Garait'') is a commune and the prefecture of the Creuse department in the Nouvelle-Aquitaine region in central France. Geography Guéret is a light industrial town, the largest in the department, with a big woodland a ...

France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

, the son of a military accountant. After taking the baccalaureate in 1849, he studied mathematics in

Bourges Bourges ( ; ; ''Borges'' in Berrichon) is a commune in central France on the river Yèvre (Cher), Yèvre. It is the capital of the Departments of France, department of Cher (department), Cher, and also was the capital city of the former provin ...

, near where his family lived, and after continuing his studies in

Paris Paris () is the Capital city, capital and List of communes in France with over 20,000 inhabitants, largest city of France. With an estimated population of 2,048,472 residents in January 2025 in an area of more than , Paris is the List of ci ...

entered the

École Polytechnique (, ; also known as Polytechnique or l'X ) is a ''grande école'' located in Palaiseau, France. It specializes in science and engineering and is a founding member of the Polytechnic Institute of Paris. The school was founded in 1794 by mat ...

in 1853. He served as a lieutenant in the French artillery in the

Second Italian War of Independence The Second Italian War of Independence, also called the Sardinian War, the Austro-Sardinian War, the Franco-Austrian War, or the Italian War of 1859 (Italian: ''Seconda guerra d'indipendenza italiana''; German: ''Sardinischer Krieg''; French: ...

, in 1859, and became a captain in 1863. He continued to serve in the military, but shifted from the artillery to the supply corps; he served in Africa, became governor of a military hospital in Algeria, participated in the

Franco-Prussian War The Franco-Prussian War or Franco-German War, often referred to in France as the War of 1870, was a conflict between the Second French Empire and the North German Confederation led by the Kingdom of Prussia. Lasting from 19 July 1870 to 28 Janua ...

in 1870, and eventually became an

intendant An intendant (; ; ) was, and sometimes still is, a public official, especially in France, Spain, Portugal, and Latin America. The intendancy system was a centralizing administrative system developed in France. In the War of the Spanish Success ...

in Orléans before retiring in 1889. His military decorations include the cross and officer's rosette of the

Legion of Honour The National Order of the Legion of Honour ( ), formerly the Imperial Order of the Legion of Honour (), is the highest and most prestigious French national order of merit, both military and Civil society, civil. Currently consisting of five cl ...

, awarded in 1868 and 1886 respectively. Beginning in 1879, Delannoy began a correspondence with

Édouard Lucas __NOTOC__ François Édouard Anatole Lucas (; 4 April 1842 – 3 October 1891) was a French mathematician. Lucas is known for his study of the Fibonacci sequence. The related Lucas sequences and Lucas numbers are named after him. Biography Luc ...

on the subject of

recreational mathematics Recreational mathematics is mathematics carried out for recreation (entertainment) rather than as a strictly research-and-application-based professional activity or as a part of a student's formal education. Although it is not necessarily limited ...

and

probability theory Probability theory or probability calculus is the branch of mathematics concerned with probability. Although there are several different probability interpretations, probability theory treats the concept in a rigorous mathematical manner by expre ...

; he eventually published eleven mathematics articles. Along with his mathematical interests, Delannoy wrote about local history, painted, and from 1896 to 1915 served as the president of the Société des Sciences Naturelles et archéologiques de la Creuse.

References

{{DEFAULTSORT:Delannoy, Henri-Auguste 1833 births 1915 deaths French mathematicians Officers of the Legion of Honour