If God's true name were a sequence of four letters, two vowels and two consonants, the number of possibilities is not difficult to calculate. But, as José Moya points out, perhaps the morphological and phonetic rules of Spanish should be taken into account, and in that case the number is significantly smaller.
Of the approximately 93,000 words in the Spanish language, how many are four letters? I suggest looking for a “Fermian” approach to this question.