In many verses in the Qur'an, it is mentioned that angels prostrated to Prophet Adam. However, this issue is explained in more detail in the 30th and 32nd verses of Surah al-Baqarah: “And [mention, O Muhammad], when your Lord said to the angels, "Indeed, I will make upon the earth a successive authority." They said, "Will You place upon it one who causes corruption therein and sheds blood, while we declare Your praise and sanctify You?" Allah said, "Indeed, I know that which you do not know." And He taught Adam the names - all of them. Then He showed them to the angels and said, "Inform Me of the names of these, if you are truthful." They said, "Exalted are You; we have no knowledge except what You have taught us. Indeed, it is You who is the Knowing, the Wise."” (Baqarah, 2/30-32)

The prostration of angels to Prophet Adam happened with the command of Allah (swt). Prostration to Prophet Adam is a sign of respect and reverence that draws attention to his superior qualities. In other words, prostration to the Prophet Adam is not for the purpose of worship, it is a requirement of obedience to Allah's order and devotion to Him. 

In verses and hadiths, angels performing different tasks are mentioned. Four archangels, angels that carry the Throne, the ones that are around the Throne, scribe angels, keepers in heaven and hell are some of them. However, in none of these sources is a number stated to indicate the number of angels. Therefore, no one but Allah (swt) knows their number. In this respect, Qur'an says And none knows the soldiers of your Lord except Him.” (Muddaththir, 74/31) 

The number of angels is hidden in the knowledge of Almighty Allah (swt). However, based on the hadiths of the Prophet Muhammad (saw), it is possible to say that the number of angels is too high for the human mind to comprehend. (Bukhari, Bad'ul-Halq, 6; Muslim, Iman, 264.)