oblong number

An integer of the form $n\cdot (n+1)$ or $n^2+n$. The partial sum

$$\sum _{i=0}^{n}2i$$

works, too. From this it follows that one can also multiply the $n$th triangular number. Plenty of other relations to various polygonal numbers can be obtained.

The first few terms are 0, 2, 6, 12, 20, 30, 42, 56, 72, 90, 110, and are listed in A002378 of Sloane’s OEIS.

Title	oblong number
Canonical name	OblongNumber
Date of creation	2013-03-22 15:50:19
Last modified on	2013-03-22 15:50:19
Owner	CompositeFan (12809)
Last modified by	CompositeFan (12809)
Numerical id	4
Author	CompositeFan (12809)
Entry type	Definition
Classification	msc 11D85
Synonym	heteromecic number
Synonym	pronic number