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A053672
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Least number coprime to n, n+1, n+2 and n+3.
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8
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5, 7, 7, 11, 11, 5, 11, 7, 7, 7, 5, 11, 11, 11, 7, 5, 7, 11, 13, 13, 5, 7, 7, 7, 11, 5, 11, 11, 7, 7, 5, 13, 13, 11, 11, 5, 7, 7, 11, 11, 5, 13, 7, 7, 7, 5, 11, 11, 11, 7, 5, 7, 13, 13, 13, 5, 7, 7, 7, 11, 5, 11, 17, 7, 7, 5, 11, 11, 11, 11, 5, 7, 7, 13, 17, 5, 17, 7, 7, 7, 5, 11, 11, 11, 7
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OFFSET
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1,1
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LINKS
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FORMULA
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MATHEMATICA
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a[n_] := (k = 5; While[ ! (CoprimeQ[k, n] && CoprimeQ[k, n+1] && CoprimeQ[k, n+2] && CoprimeQ[k, n+3]), k++]; k); Table[a[n], {n, 1, 85}](* Jean-François Alcover, Nov 30 2011 *)
Table[Module[{k=3}, While[!And@@CoprimeQ[n+Range[0, 3], Prime[k]], k++]; Prime[k]], {n, 90}] (* Harvey P. Dale, May 10 2012 *)
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PROG
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(Haskell)
import Data.List (elemIndex)
import Data.Maybe (fromJust)
a053672 n = 2 + fromJust
(elemIndex 1 $ map (gcd $ foldl1 lcm $ take 4 [n..]) [2..])
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CROSSREFS
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KEYWORD
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nonn,easy,nice
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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