egison-3.7.8: sample/math/number/zeta.egi

(define $zeta
  (lambda [$n]
    (rtof (foldl + 0 (take n (map (lambda [$n] (* (/ 1 n) (/ 1 n))) nats))))))

(test (zeta 100))
(test (zeta 1000))
(test (zeta 10000))

(test (/ (* pi pi) 6))