Letters of Names of Numbers in Alphabetical Order/English

Theorem

When written in English, the only integer the letters of whose name appear in alphabetical order is:

$40$: forty

Historical Note

David Wells reports in Curious and Interesting Numbers, 2nd ed. from $1997$ that this observation is attributed to a Richard Harris, but no corroboration can be found confirming this, or even who Richard Harris may have been.

Sources

• 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $40$