1×20

1×20, read as "one by twenty," is typically used to indicate either a product of the numbers 1 and 20 or a dimension expressed as one unit by twenty units. In arithmetic, 1×20 equals 20, illustrating the multiplicative identity property: multiplying by 1 does not change the other factor. By symmetry, 20×1 also equals 20.

When used as a dimension or shape, 1×20 denotes a rectangle with one row and twenty columns, or a 1-by-20 matrix in linear algebra, which is a row vector with twenty elements.

In electronics and hardware, 1×20 often describes a connector layout, such as a 1×20 pin header consisting of twenty pins in a single row. This notation helps convey the arrangement of pins or contacts in a compact form.