In the Quran, many Surahs (29 out of 114) start with seemingly random letters, some scholars profess that these letters have hidden meaning; yet, there is nothing in the Quran nor the Hadiths that tend towards this.
Others say that each letter contains a numerical value attached to it. Where the story of the Jews of Medina that said the reign of Muhammad will last 71 years because the first Surah revealed in Medina begins with Alif, Lam, Mim (Alif = 1, Lam = 30 and Mim =40). And we know by now that there was Islamic rule for well over 1300 years (fall of the Ottoman Empire), and Muslims are found in numbers across all continents. Therefore, none of this is supported factually nor by any teachings of the prophet.
The most plausible explanation is since the Quran was revealed in Arabic and that Arabs are the most knowledgeable in that field; therefore, with the same letters, they should come up with something similar in greatness to the Quran. It is the alphabet challenge that has never been taken up in over 1400 years, or more likely, no one has ever succeeded; nor will anyone ever succeed.
Overwhelmingly, in Surahs that start with letters, the verse right after mentions the greatness of the Quran, i.e. the fact that it is inimitable.
Alif, Lam, Meem.
This is the Book about which there is no doubt, a guidance for those conscious of Allah –
Surah Al-Baqarah (2 – 1-2)
Alif, Lam, Ra. [This is] a Book whose verses are perfected and then presented in detail from [one who is] Wise and Acquainted.
Surah Hud (11 – 1)
Alif, Lam, Ra. [This is] a Book which We have revealed to you, [O Muhammad], that you might bring mankind out of darknesses into the light by permission of their Lord – to the path of the Exalted in Might, the Praiseworthy –
Surah Ibrahim (14 – 1)
Alif, Lam, Meem.
[This is] the revelation of the Book about which there is no doubt from the Lord of the worlds.
Or do they say, “He invented it”? Rather, it is the truth from your Lord, [O Muhammad], that you may warn a people to whom no warner has come before you [so] perhaps they will be guided.
Surah As-Sajdah (32 – 1-3)
Can any other book pretend to that?
And it was not [possible] for this Qur’an to be produced by other than Allah, but [it is] a confirmation of what was before it and a detailed explanation of the [former] Scripture, about which there is no doubt, from the Lord of the worlds.
Or do they say [about the Prophet], “He invented it?” Say, “Then bring forth a surah like it and call upon [for assistance] whomever you can besides Allah, if you should be truthful.”
Surah Younus (10 – 37-38)
Then would you possibly leave [out] some of what is revealed to you, or is your breast constrained by it because they say, “Why has there not been sent down to him a treasure or come with him an angel?” But you are only a warner. And Allah is Disposer of all things.
Or do they say, “He invented it”? Say, “Then bring ten surahs like it that have been invented and call upon [for assistance] whomever you can besides Allah, if you should be truthful.”
And if they do not respond to you – then know that the Qur’an was revealed with the knowledge of Allah and that there is no deity except Him. Then, would you [not] be Muslims?
Surah Hud (11 – 12-14)