triangular number

Noun

 * 1)  Any integer that is the sum of n natural numbers from 1 to n.
 * Ten is a triangular number being the sum of 1, 2, 3, and 4.

Translations

 * Chinese:
 * Mandarin:
 * Dutch: driehoeksgetal
 * Esperanto: triangula nombro
 * Finnish: kolmioluku
 * German:
 * Hungarian: háromszögszám
 * Italian: numero triangolare
 * Japanese: 三角数
 * Latin: numerus triangularis
 * Polish: liczba trójkątna
 * Russian: треуго́льное число́
 * Spanish: número triangular
 * Tagalog: bilang na tatsihain