Sha256: c2be447fe8ad31b4d65f5cd8743b0fcb6724a2ac13d9c1378b79c1e50cb97bb0
Contents?: true
Size: 501 Bytes
Versions: 396
Compression:
Stored size: 501 Bytes
Contents
module Prime (nth) where
nth :: Int -> Maybe Integer
nth x
| x <= 0 = Nothing
| otherwise = Just $ nth' x
nth' :: Int -> Integer
nth' = (primes !!) . pred
-- all primes > 5 are in the form of 6n+1 or 6n+5 (for n >= 1)
primes :: [Integer]
primes = 2 : 3 : 5 : filter (go $ drop 2 primes) candidates
where
candidates = [x | n6 <- [6, 12 ..], x <- [n6 + 1, n6 + 5]]
go (p:ps) n = case n `quotRem` p of
(_, 0) -> False
(q, _) -> q < p || go ps n
go _ _ = undefined
Version data entries
396 entries across 396 versions & 1 rubygems