Nicomachus of Gerasa (Νικόμαχος; 60-120 AD) was an Ancient Greek Neopythagorean philosopher from Gerasa, in the Roman province of Syria (now Jerash, Jordan). Like many Pythagoreans, Nicomachus wrote about the mystical properties of numbers, best known for his works Introduction to Arithmetic and Manual of Harmonics, which are an important resource on Ancient Greek mathematics and Ancient Greek music in the Roman period. Nicomachus' work on arithmetic became a standard text for Neoplatonic education in Late antiquity, with philosophers such as Iamblichus and John Philoponus writing commentaries on it. A Latin paraphrase by Boethius of Nicomachus's works on arithmetic and music became standard textbooks in medieval education.
Little is known about the life of Nicomachus except that he was a Pythagorean who came from Gerasa. His Manual of Harmonics was addressed to a lady of noble birth, at whose request Nicomachus wrote the book, which suggests that he was a respected scholar of some status. He mentions his intent to write a more advanced work, and how the journeys he frequently undertakes leave him short of time.The approximate dates in which he lived (100 AD) can only be estimated based on which other authors he refers to in his work, as well as which later mathematicians who refer to him. He mentions Thrasyllus in his Manual of Harmonics, and his Introduction to Arithmetic was apparently translated into Latin in the mid 2nd century by Apuleius,while he makes no mention at all of either Theon of Smyrna's work on arithmetic or Ptolemy's work on music, implying that they were either later contemporaries of lived in the time after he did.
Historians consider Nicomachus a Neopythagorean based on his tendency to view numbers as having mystical properties rather than their mathematical properties, citing an extensive amount of Pythagorean literature in his work, including works by Philolaus, Archytas, and Androcydes.