Name: Anonymous 2009-06-15 15:56
for(int a1=1,a2=1,i=scanf_s("%d",&i)+i-1;(i--)>2; a1=(a2+=a1)-a1,(i==2)?printf_s("Result=%d\n",a2):NULL)
primes = 2 : 3 : 5 : 7 : [k + r | k <- [0, 30..], r <- [11, 13, 17, 19, 23, 29, 31, 37], primeTest (k + r)]
where primeTest n = all ((0 /=) . mod n) . takeWhile ((n >=) . join (*)) $ drop 3 primes
bitCount 0 = 0
bitCount n = bitCount (shiftR n 1) + n .&. 1
swing n | n < 33 = genericIndex smallOddSwing n
| True = product pList
where smallOddSwing = [1, 1, 1, 3, 3, 15, 5, 35, 35, 315, 63, 693, 231, 3003, 429, 6435, 6435, 109395, 12155, 230945, 46189, 969969, 88179, 2028117, 676039, 16900975, 1300075, 35102025, 5014575, 145422675, 9694845, 300540195, 300540195]
pListA q p prime = let x = div q prime in case x of
0 -> case p of
1 -> []
_ -> [p]
_ -> pListA x (p * prime ^ (mod x 2)) prime
pListB = (filter ((1==) . flip (.&.) 1 . div n) . takeWhile (<= div n 3) $ dropWhile ((<= n) . join (*)) primes)
pListC = takeWhile (<= n) $ dropWhile (<= shiftR n 1) primes
pList = (concatMap (pListA n 1) . takeWhile ((n >=) . join (*)) $ tail primes) ++ pListB ++ pListC
recFactorial n | n < 2 = 1
| True = join (*) (recFactorial $ div n 2) * swing n
factorial :: Int -> Integer
factorial n | n < 20 = product [2..fromIntegral n]
| True = shiftL (recFactorial $ fromIntegral n) (n - bitCount n)product([], 1).
product([H|T], X) :- product(T, Y), X is H * Y.
factorial(N, R) :- numlist(2, N, Ns), product(Ns, R).