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;;;;
;; Even Fibonacci numbers
;; Problem 2
;;
;; Each new term in the Fibonacci sequence is generated by adding the previous two terms. By
;; starting with 1 and 2, the first 10 terms will be:
;; 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
;; By considering the terms in the Fibonacci sequence whose values do not exceed four
;; million, find the sum of the even-valued terms.
;;;;
(def fib
(memoize (fn [n]
(case n
0 1
1 1
(+' (fib (-' n 1)) (fib (-' n 2)))))))
(def +top+ 4000000)
(def result
(reduce +
(for [x (range 1 1000)
:let [f (fib x)]
:when (= (mod f 2) 0)
:while (< f +top+)]
f)))
(println result)
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