A053671 Least number coprime to n, n+1 and n+2.

5, 5, 7, 7, 11, 5, 5, 7, 7, 7, 5, 5, 11, 11, 7, 5, 5, 7, 11, 13, 5, 5, 7, 7, 7, 5, 5, 11, 7, 7, 5, 5, 13, 11, 11, 5, 5, 7, 7, 11, 5, 5, 7, 7, 7, 5, 5, 11, 11, 7, 5, 5, 7, 13, 13, 5, 5, 7, 7, 7, 5, 5, 11, 7, 7, 5, 5, 11, 11, 11, 5, 5, 7, 7, 13, 5, 5, 7, 7, 7, 5, 5, 11, 11, 7, 5, 5, 7, 11, 11, 5, 5

Offset: 1

Author

Henry Bottomley, Feb 15 2000

Keywords

• nonn
• easy
• nice

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A053669-A053674.

Programs

Haskell

a053671 n = f $ drop 2 a000040_list where
   f (p:ps) | (n `mod` p) * ((n+1) `mod` p) * ((n+2) `mod` p) > 0 = p
            | otherwise = f ps
-- Reinhard Zumkeller, Mar 19 2011

Mathematica

a[n_] := (k = 5; While[! (CoprimeQ[k, n] && CoprimeQ[k, n+1] && CoprimeQ[k, n+2]), k++]; k); Table[a[n], {n, 1, 92}] (* Jean-François Alcover, Nov 30 2011 *)
lnc[n_]:=Module[{k=5,c=n+{0,1,2}},While[!And@@CoprimeQ[k,c],k=k+2];k]; Array[lnc,100] (* Harvey P. Dale, Mar 01 2015 *)

Extensions

More terms from James Sellers, Feb 22 2000