The loneliest number is often referred to as 'ONE' due to its solitary nature. It is the smallest natural number and the only ONE that is neither a prime nor composite number. It is the first and only positive integer and the first and only odd number. It is also the only number that is neither a perfect square nor a perfect cube. The loneliest number has been used in popular culture, most notably in the song 'ONE' by Three Dog Night.