The sieve of Sundaram: Difference between revisions
→{{header|Haskell}}: Added a draft version in Haskell
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As a check, the 1,000,000 Sundaram prime would again have been 15,485,867
</pre>
=={{header|Haskell}}==
<lang haskell>import Data.List (intercalate, transpose)
import Data.List.Split (chunksOf)
import qualified Data.Set as S
import Text.Printf (printf)
--------------------- SUNDARAM PRIMES --------------------
sundaram :: Integral a => a -> [a]
sundaram n =
[ succ (2 * x)
| x <- [1 .. m],
x `S.notMember` excluded
]
where
m = div (pred n) 2
excluded =
S.fromList
[ 2 * i * j + i + j
| let fm = fromIntegral m,
i <- [1 .. floor (sqrt (fm / 2))],
let fi = fromIntegral i,
j <- [i .. floor ((fm - fi) / succ (2 * fi))]
]
nSundaramPrimes ::
(Integral a1, RealFrac a2, Floating a2) => a2 -> [a1]
nSundaramPrimes n =
sundaram $ floor $ (2.4 * n * log n) / 2
--------------------------- TEST -------------------------
main :: IO ()
main = do
putStrLn "First 100 Sundaram primes (starting at 3):\n"
(putStrLn . table " " . chunksOf 10) $
show <$> nSundaramPrimes 100
table :: String -> [[String]] -> String
table gap rows =
let ws = maximum . fmap length <$> transpose rows
pw = printf . flip intercalate ["%", "s"] . show
in unlines $ intercalate gap . zipWith pw ws <$> rows</lang>
{{Out}}
<pre>First 100 Sundaram primes (starting at 3):
3 5 7 11 13 17 19 23 29 31
37 41 43 47 53 59 61 67 71 73
79 83 89 97 101 103 107 109 113 127
131 137 139 149 151 157 163 167 173 179
181 191 193 197 199 211 223 227 229 233
239 241 251 257 263 269 271 277 281 283
293 307 311 313 317 331 337 347 349 353
359 367 373 379 383 389 397 401 409 419
421 431 433 439 443 449 457 461 463 467
479 487 491 499 503 509 521 523 541 547</pre>
=={{header|Julia}}==
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