Psi (letter)

Psi (uppercase/lowercase Ψ ψ) is the 23rd letter of the Greek alphabet. It is used to represent the "ps" sound in Ancient and Modern Greek. In the system of Greek numerals, it has a value of 700. Letters that came from it include Cyrillic Ѱ.

Greek alphabet
Αα Alpha Νν Nu Ββ Beta Ξξ Xi Γγ Gamma Οο Omicron Δδ Delta Ππ Pi Εε Epsilon Ρρ Rho Ζζ Zeta Σσς Sigma Ηη Eta Ττ Tau Θθ Theta Υυ Upsilon Ιι Iota Φφ Phi Κκ Kappa Χχ Chi Λλ Lambda Ψψ Psi Μμ Mu Ωω Omega
History
Archaic local variants Diacritics Ligatures Numerals ϛ (6) ϟ (90) ϡ (900)
Use in other languages
Bactrian Coptic Albanian
Related topics
Use as scientific symbols
Book Category Commons

In mathematics, the uppercase ${\displaystyle \Psi }$ is used as a variable for sets of sentences (in logic), and the lowercase ${\displaystyle \psi }$ is used to represent the sum of reciprocals of Fibonacci numbers.[1] Other applications include the polygamma function, the gamma function and the super golden ratio.[2]