Well they are very very many.Their numbers are never entirely specified apart from Grimoires and if you are into knowing their names and divisions take a look at
As regards to the latter there are some astranomically unbeleivable figures given for example(among several therein)
"Caspiel is the Chiefest Emperor Ruling the South who hath 200 great Dukes & 400 lesser Dukes under him besides 1,000,200,000,000 of Ministring Spirits which are much inferior & whereof we [saith Solomon] shall make no mention but only of these 12 being the chief Dukes & their seals for they are sufficient for practise. Each of these 12 Dukes have 2660 under Dukes apeace to Attend them, whereof some of
them come along with him when he is invocated but they are very stubborn & churlish. The seals of his Dukes follow."
As regards the Bible an example that is worthy is the Exorcism of the Gerasene demoniac in Mark 5 .Here a demon probably speaks for several calling himself "Legion, for we are many"....They plead with Jesus to let them into pigs and the pigs nearby numbered 2000 and after they left the man they entered the pigs and drowned them all by rushing down into the lake.
Now for demons out of one man to posess 2000 pigs either means they were really many and posessed each pig (demon for pig) or it could be that one demon can posess several animated creatures and men who are in close proximity to each other simultaneously.
Both scenarios could be true as angels hold power beyond our own
Real number crunching is imposiible but the truth is that they are really numerous and contrary to popular beleif they are not departed bad souls or good souls.They have maintained their number since their collective creation being immortal and unable to reproduce...Though genesis 6 seems to purport that they tried.
According to the book of Enoch some 200 who fell had sex with women but only the 28 prominent leaders are mentioned as follows:
Semyaza,Azazel,Amazarak,Armers,Barkaya... Akibeel,Tamiel,Penemue, Kasdeja,Gadreel,Ramuell,Danel, Azkeel,Saraknyal,Asael,Batraal,Anane,Zav...
Confusion also arises as to wether Satan/Lucifer is also Beelzebub,Belial,Leviathan by name or wether these names are atributed to his senior 'leutenants'.Many satanists and oculltists take the names as seperate entities all under Lucifer/Satan
All in all they are very many