Solved 16 and 20

src/euler/16.clj

@@ -5,5 +5,3 @@
   [n]
   (.toPlainString (BigDecimal. (Math/pow 2 n))))
 
-(defn sum-digits [n]
-  (reduce + (map #(Integer/parseInt (str %)) (seq (two-str n)))))

src/euler/20.clj

@@ -0,0 +1,12 @@
+(ns euler.20
+  (:use [euler.common]))
+
+(defn ! [x]
+  (letfn [(factorial [x product]
+    (if (zero? x)
+      product
+      (recur (dec x) (* x product))))]
+    (factorial (bigint x) 1)))
+
+(defn sum-! [x]
+  (sum-digits (str (! x))))

src/euler/common.clj

@@ -3,4 +3,7 @@
 
 (defn arithmetic-series [n]
   (if (< n 0) (throw (ArithmeticException. "only supports natural numbers")))
-  (* n (mean [n 1])))
+  (* n (mean [n 1])))
+
+(defn sum-digits [n]
+  (reduce + (map #(Integer/parseInt (str %)) (seq n))))

src/euler/2.clj → src/euler/fibs.clj

@@ -1,4 +1,4 @@
-(ns euler.2)
+(ns euler.fibs)
 
 ; from Programming Clojure, p. 157
 (defn fibonacci-seq []
@@ -16,3 +16,5 @@
 (defn fibonacci [k]
   (last (take k (fibonacci-seq))))
 
+(defn fib-with-term-sized [k]
+  (count (take-while #(< (count (str %)) k) (fibonacci-seq))))

test/euler/test/16.clj

@@ -1,5 +1,6 @@
 (ns euler.test.16
   (:use [euler.16]
+		[euler.common]
         [clojure.test]))
 
 (deftest test-two-str
@@ -8,6 +9,6 @@
 )
 
 (deftest test-sum-digits
-  (is (= 26 (sum-digits 15)))
-  (is (= 1366 (sum-digits 1000)))
+  (is (= 26 (sum-digits (two-str 15))))
+  (is (= 1366 (sum-digits (two-str 1000))))
 )

test/euler/test/2.clj

@@ -1,5 +1,5 @@
 (ns euler.test.2
-  (:use [euler.2]
+  (:use [euler.fibs]
 		[clojure.test]))
 
 (deftest test-fibonacci-terms

test/euler/test/20.clj

@@ -0,0 +1,15 @@
+(ns euler.test.20
+  (:use [clojure.test]
+	    [euler.common]
+	    [euler.20]))
+
+(deftest test-!
+  (is (= 1 (! 0)))
+  (is (= 1 (! 1)))
+  (is (= 6 (! 3)))
+)
+
+(deftest test-sum-!
+  (is (= 27 (sum-! 10)))
+  (is (= 648 (sum-! 100)))
+)

test/euler/test/25.clj

@@ -0,0 +1,10 @@
+(ns euler.test.25
+  (:use [clojure.test] 
+        [euler.fibs]))
+
+
+(deftest test-fib-with-term-sized
+  (is (= 12 (fib-with-term-sized 3)))
+  (is (= 45 (fib-with-term-sized 10)))
+  (is (= 476 (fib-with-term-sized 100)))
+)