oblong number
mathematics
Quick Summary
Oblong numbers formed by doubling triangular numbers
Figure 2: Oblong numbers formed by doubling triangular numbers.
Oblong numbers, also known as pronic numbers, are a type of figurate number. They represent the quantity of dots that can be arranged in a rectangular array where each row has one more dot than each column.1
The first few oblong numbers are 2, 6, 12, 20, and 30. These numbers can be calculated by multiplying two consecutive integers:
* 2 = 1 × 2
* 6 = 2 × 3
* 12 = 3 × 4
* 20 = 4 × 5
* 30 = 5 × 6
Oblong numbers can also be found by summing consecutive even numbers or by doubling any triangular number.1
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