The Pochhammer symbol (x)_n | congruent | (Γ(x + n))/(Γ(x)) | = | x(x + 1)...(x + n - 1) (Abramowitz and Stegun 1972, p. 256; Spanier 1987; Koepf 1998, p. 5) for n>=0 is an unfortunate notation used in the theory of special functions for the rising factorial, also known as the rising factorial power or ascending Factorial. The Pochhammer symbol is implemented in the Wolfram Language as Pochhammer[x, n].