Rectangular numbers are of the form n(n+1) for n = 1, 2, 3, 4, 5, 6, ... The first few rectangular numbers are: 2, 6, 12, 20, 30, 42, ...
6
The question is ambiguous since a rectangular pyramid and a rectangular prism will have different numbers of flat surfaces. There is no indication in the question which shape is intended.
It is a matrix or a determinant.
matrix
Rectangular numbers are a subset of composite numbers. The squares of prime numbers will be composite but not rectangular.
The second and third rectangular numbers are 6 and 12
There is no such formula. Rectangular numbers are composite numbers and there is no known formula that will generate either composite numbers or prime numbers.
So far I know that 120 is a rectangular number
Rectangular numbers are of the form n(n+1) for n = 1, 2, 3, 4, 5, 6, ... The first few rectangular numbers are: 2, 6, 12, 20, 30, 42, ...
42
A row of numbers, a column of numbers or a rectangular layout of numbers.
101
Apart fro the fact that no number is triangler, none of the numbers listed are rectangular and triangular.
They are simply rectangular arrays of numbers.
6
12