Demonstration, with Cuisenaire rods, that the composite number 10 is equidigital: 10 has two digits, and 2×5 has two digits (1 is excluded)
An equidigital number is a number that has the same number of digits as the number of digits in its prime factorization, including exponents but excluding exponents equal to 1. For example, in base-10 arithmetic 1, 2, 3, 5, 7, and 10 (2×5) are equidigital numbers. All prime numbers are equidigital numbers in any base.
A number that is either equidigital or frugal is said to be economical.
