Pseudomonarchia Daemonum
Johann Weyer, in his "Pseudomonarchia Daemonum" (1583), after a complicated system of hierarchies and calculations, estimated the number of demons as 4,439,622, divided into 666 legions, each legion composed of 6,666 demons, and all of them ruled by 66 hellish dukes, princes, kings, etc. "The Lesser Key of Solomon" (17th century) copied the division in legions from "Pseudomonarchia Daemonum" but added more demons, and so more legions. It is suggestive that both Spina and Weyer used "666" and other numbers composed by more than one "6" to calculate the number of demons (133,316,666 demons, 666 legions, 6,666 demons in each legion, 66 rulers).