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A073251
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Numbers n such that n, n+1 and n+2 are nonprime and squarefree.
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2
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33, 85, 93, 141, 185, 201, 213, 217, 253, 265, 285, 301, 321, 393, 445, 453, 469, 481, 517, 533, 553, 581, 589, 609, 633, 669, 697, 705, 713, 753, 777, 789, 793, 805, 813, 869, 893, 897, 901, 913, 921, 933, 957, 985, 993, 1001, 1005, 1041, 1045, 1065, 1113
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OFFSET
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1,1
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COMMENTS
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n-1 and n+3 are not squarefree. Proof: n is odd, otherwise n or n+2 would be divisible by 4. Thus n+1 is even and not divisible by 4, hence n-1 and n+3 are divisible by 4.
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LINKS
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Table of n, a(n) for n=1..51.
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MATHEMATICA
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f[upto_]:=Module[{pp=PrimePi[upto], n}, lst=Partition[Complement[Range[upto], Prime[Range[pp]]], 3, 1]; Transpose[Select[lst, And@@SquareFreeQ/@#&]][[1]]]; f[1200] (* From Harvey P. Dale, Mar 21 2011 *)
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CROSSREFS
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Cf. A000469, A005117, A007675, A073249, A073250, A121495.
Sequence in context: A044552 A045939 A056809 * A005238 A052214 A063838
Adjacent sequences: A073248 A073249 A073250 * A073252 A073253 A073254
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KEYWORD
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nonn
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AUTHOR
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Reinhard Zumkeller, Jul 22 2002
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EXTENSIONS
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Edited by Klaus Brockhaus, Aug 07 2006
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STATUS
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approved
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