Name for numbers of the form (x)(x±1)

Question

I would like to know if there is a formal name for numbers of the form (x)(x±1). Ie, the numbers that fall between the perfect squares: 2, 6, 12, 20, 30, etc.

Answer 1

The sequence of numbers you asked about is the OEIS sequence A002378 named

Oblong (or promic, pronic, or heteromecic) numbers: a(n) = n*(n+1).

The OEIS entry also comments

The word "pronic" (used by Dickson) is incorrect.

However, the mistake seems due to Euler and so just as his mistake in naming Pell's equation it has stuck.

There is much more information about the sequence in the OEIS entry.

Answer 2

No special name to the best of my knowledge. They can be described as products of consecutive integers. They are also twice the corresponding triangular number.