Function: zetamult
Section: transcendental
C-Name: zetamult
Prototype: Gp
Help: zetamult(s): multiple zeta value at integral s = [s1,...,sd].
Doc: For $s$ a vector of positive integers such that $s[1] \geq 2$,
 returns the multiple zeta value (MZV)
 $$\zeta(s_1,\dots, s_k) = \sum_{n_1>\dots>n_k>0} n_1^{-s_1}\dots n_k^{-s_k}.$$
 \bprog
 ? zetamult([2,1]) - zeta(3) \\ Euler's identity
 %1 = 0.E-38
 @eprog
