When a whole number is written out in words, which common word is deliberately left out?

1. Whole numbers are named period by period, from the largest period down to the ones. 2. Words such as hundred, thousand, and million are used to name each period. 3. The word and is not used when naming a whole number, unlike with decimals. 4. Thousand, million, and hundred are all needed period names, so the word left out is and. _Source: OpenStax Prealgebra (CC BY 4.0), Ch 1 "Whole Numbers", section 1.1 Introduction to Whole Numbers_