The word(s) "letters" appears 29 time(s) in 29 verse(s) in Quran in Mohsin Khan translation.

(11) Ta-Ha. [These letters are one of the miracles of the Qur'an, and none but Allah (Alone) knows their meanings].

(12) Ta-Sin-Mim. [These letters are one of the miracles of the Qur'an, and none but Allah (Alone) knows their meanings.]

(13) Ta-Sin. [These letters are one of the miracles of the Qur'an, and none but Allah (Alone) knows their meanings]. These are the Verses of the Qur'an, and (it is) a Book (that makes things) clear:

(14) Ta-Sin-Mim [These letters are one of the miracles of the Qur'an, and none but Allah (Alone) knows their meanings].

(15) Alif-Lam-Mim. [These letters are one of the miracles of the Qur'an, and none but Allah (Alone) knows their meanings.]

(16) Alif-Lam-Mim. [These letters are one of the miracles of the Qur'an, and none but Allah (Alone) knows their meanings].

(17) Alif-Lam-Mim. [These letters are one of the miracles of the Qur'an, and none but Allah (Alone) knows their meanings].

(18) Alif-Lam-Mim. [These letters are one of the miracles of the Qur'an, and none but Allah (Alone) knows their meanings].

(19) Ya-Sin. [These letters are one of the miracles of the Qur'an, and none but Allah (Alone) knows their meanings].

(20) Sad. [These letters (Sad, etc.) are one of the miracles of the Qur'an, and none but Allah (Alone) knows their meanings]. By the Qur'an full of reminding (explanations and honour for the one who believes in it).