Yap.Town

の数が少ない

the number of … is small

→ の
phrase Rare #45,423
the number of … is small の links the thing being counted to 数 (number); 少ない means “few” or “not many.”
JA: この町はレストランの数が少ない。
EN: There are few restaurants in this town.

彼は僕より友達の数が少ない。

He has fewer friends than I do.

母となる女性の数が少ない。

There are few women who become mothers.