# Project Euler 解答

## Project Euler Problem 035

Project Euler Problem 035

```import Data.Char
import Data.List
--003より
primes :: [Integer]
primes = 2 : ([3,5..] `minus` join [[p*p, p*p+2*p..] | p <- primes'])
where
primes' = 3 : ([5,7..] `minus` join [[p*p, p*p+2*p..] | p <- primes'])
join  ((x:xs):t)    = x : union xs (join (pairs t))
pairs ((x:xs):ys:t) = (x : union xs ys) : pairs t
union (x:xs) (y:ys) = case (compare x y) of
LT -> x : union  xs  (y:ys)
EQ -> x : union  xs     ys
GT -> y : union (x:xs)  ys
union  xs     []    = xs
union  []     ys    = ys
minus (x:xs) (y:ys) = case (compare x y) of
LT -> x : minus  xs  (y:ys)
EQ ->     minus  xs     ys
GT ->     minus (x:xs)  ys
minus  xs     _     = xs
factor :: Integer -> [Integer]
factor n = factorimpl n primes where
factorimpl n pri@(p:xs) =
if p*p>n then [n]
else if n`rem` p == 0 then
p:factorimpl (n `quot` p) pri
else
factorimpl n xs
divsum :: Integer -> Integer
divsum n =  (product. map tohi .group . factor) n - n where
tohi [x] = x+1
tohi l@(x:xs) = (x^(length l+1)-1) `quot` (x-1)
isprime :: Integer -> Bool
isprime nn = imp nn primes where
imp n (x:xs) = if x*x>n then True
else if rem n x==0 then False
else imp n xs

rotate :: Show a => a -> Int
rotate n = let (x:xs) = map digitToInt \$ show n in
foldl1 (\ac x -> x+ac*10) (xs++[x])
digit :: (Integral a, Num a1) => a -> a1
digit x = if x `quot` 10 /= 0 then 1 + digit (x`quot` 10) else 0
iscir :: Int -> Bool
iscir x = let n = show x in
if '0' `elem` n then False
else case length n of
0 -> True
n -> all (isprime.fromIntegral) \$ take (n+1) \$ iterate rotate x
an :: Integer -> [Integer]
an n = [x | x<-takeWhile (```
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