Jacobsthal numbers: Difference between revisions
→{{header|Haskell}}: Added a variant defined in terms of unfoldr
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[3,5,11,43,683,2731,43691,174763,2796203,715827883]
</pre>
or, defined in terms of unfoldr:
<lang haskell>import Data.List (intercalate, transpose, uncons, unfoldr)
import Data.List.Split (chunksOf)
import Data.Numbers.Primes (isPrime)
import Text.Printf (printf)
-------------------- JACOBSTHAL NUMBERS ------------------
jacobsthal = jacobsthalish [0, 1]
jacobsthalish :: [Integer] -> [Integer]
jacobsthalish = unfoldr go
where
go xs =
let Just (a, t@(b : _)) = uncons xs
in Just (a, t <> [2 * a + b])
--------------------------- TEST -------------------------
main :: IO ()
main =
mapM_
(putStrLn . format)
[ ( "terms of the Jacobsthal sequence",
30,
jacobsthal
),
( "Jacobsthal-Lucas numbers",
30,
jacobsthalish [2, 1]
),
( "Jacobsthal oblong numbers",
20,
zipWith (*) jacobsthal (tail jacobsthal)
),
( "Jacobsthal primes",
10,
filter isPrime jacobsthal
)
]
format :: (String, Int, [Integer]) -> String
format (k, n, xs) =
show n <> (' ' : k) <> ":\n"
<> table
" "
(chunksOf 5 $ show <$> take n xs)
table :: String -> [[String]] -> String
table gap rows =
let ws = maximum . fmap length <$> transpose rows
pw = printf . flip intercalate ["%", "s"] . show
in unlines $ intercalate gap . zipWith pw ws <$> rows</lang>
{{Out}}
<pre>30 terms of the Jacobsthal sequence:
0 1 1 3 5
11 21 43 85 171
341 683 1365 2731 5461
10923 21845 43691 87381 174763
349525 699051 1398101 2796203 5592405
11184811 22369621 44739243 89478485 178956971
30 Jacobsthal-Lucas numbers:
2 1 5 7 17
31 65 127 257 511
1025 2047 4097 8191 16385
32767 65537 131071 262145 524287
1048577 2097151 4194305 8388607 16777217
33554431 67108865 134217727 268435457 536870911
20 Jacobsthal oblong numbers:
0 1 3 15 55
231 903 3655 14535 58311
232903 932295 3727815 14913991 59650503
238612935 954429895 3817763271 15270965703 61084037575
10 Jacobsthal primes:
3 5 11 43 683
2731 43691 174763 2796203 715827883</pre>
=={{header|J}}==
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