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A073251 Numbers n such that n, n+1 and n+2 are nonprime and squarefree. 3
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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.

LINKS

Table of n, a(n) for n=1..51.

MATHEMATICA

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] (* Harvey P. Dale, Mar 21 2011 *)

CROSSREFS

Cf. A000469, A005117, A007675, A073249, A073250, A121495.

Sequence in context: A044552 A045939 A056809 * A005238 A052214 A063838

Adjacent sequences:  A073248 A073249 A073250 * A073252 A073253 A073254

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Jul 22 2002

EXTENSIONS

Edited by Klaus Brockhaus, Aug 07 2006

STATUS

approved

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Last modified December 3 07:27 EST 2016. Contains 278698 sequences.