Hello, Here is a short (16 lines) and readable Haskell'98 solution. I haven't optimized it or tested it much. When compiled with ghc(6.4.1) -O2, it takes about 10s to compute the answer for 9, on my P3 366MHz machine. It seems to use about 16K of memory. -Iavor import System(getArgs) flop xs@(x:_) = reverse (take x xs) ++ drop x xs flops xs = takeWhile ((1 /=) . head) (iterate flop xs) perms xs = foldr (concatMap . ins) [[]] xs ins x [] = [[x]] ins x (y:ys) = (x:y:ys) : map (y:) (ins x ys) pfannkuchen x = maximum (map (length . flops) (perms [1..x])) main = do a:_ <- getArgs let n = read a :: Int putStrLn (unlines (map show (take 30 (perms [1..n])))) print (pfannkuchen n)