Inverted nuns are found in nine passages of the Masoretic Text of the Bible. The exact shape varies between different manuscripts and printed editions. In many manuscripts, a reversed nun is found—referred to as a "nun hafucha" by the Masoretes. In some earlier printed editions, they are shown as the standard nun upside down or rotated, because the printer did not want to bother to design a character to be used only nine times.  These are sometimes referred to in rabbinical literature as "simaniyot" (markers).

Psalm 145 is an alphabetic acrostic, the initial letter of each verse being the Hebrew alphabet in sequence. (For this purpose, the usual Hebrew numbering of verse 1, which begins with the title, "A Psalm of David", is ignored in favor of the non-Hebrew numbering which treats verse 1 as beginning (Aromimkhaw, "I will exalt You"). But there is no verse beginning with the letter nun (?), which would come between verses 13 and 14.  That the absence of a verse beginning with that letter was noticed and was undisputed even in antiquity.

However, the Septuagint provides a verse at this point which commences (in Hebrew) with nun— "Faithful is YHVH in all His ways, and merciful in all His works". .