Let f be a function that has derivatives of all orders at x=c (i.e. f is infinitely differentiable, or smooth, at c). The Taylor series of f centered at c is the power series
n=0∑∞n!f(n)(c)(x−c)n=f(c)+f′(c)(x−c)+2!f′′(c)(x−c)2+3!f′′′(c)(x−c)3+⋯,
where f(n)(c) denotes the n-th derivative of f evaluated at c (with f(0)(c)=f(c) and 0!=1).
The coefficients cn=f(n)(c)/n! are called the Taylor coefficients of f at c.