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A073247
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Squarefree numbers n such that n-1 and n+1 are not squarefree.
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10
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17, 19, 26, 51, 53, 55, 89, 91, 97, 127, 149, 151, 161, 163, 170, 197, 199, 233, 235, 241, 249, 251, 269, 271, 293, 295, 305, 307, 337, 339, 341, 349, 362, 377, 379, 413, 415, 449, 451, 485, 487, 489, 491, 521, 523, 530, 551, 557, 559, 577, 579, 593, 595
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OFFSET
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1,1
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COMMENTS
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Probably 11*n < a(n) < 12*n for n > 189. - Charles R Greathouse IV, Nov 05 2017
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LINKS
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Christopher E. Thompson, Table of n, a(n) for n = 1..10000
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MAPLE
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sf:= select(numtheory:-issqrfree, [$1..1000]):
map(t -> `if`(sf[t-1]=sf[t]-1 or sf[t+1]=sf[t]+1, NULL, sf[t]), [$2..nops(sf)-1]); # Robert Israel, Feb 01 2016
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MATHEMATICA
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Reap[For[n = 0, n <= 1000, n++, If[SquareFreeQ[n] && !SquareFreeQ[n-1] && !SquareFreeQ[n+1], Sow[n]]]][[2, 1]] (* Jean-François Alcover, Feb 26 2019 *)
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PROG
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(PARI) is(n)=!issquarefree(n-1) && issquarefree(n) && !issquarefree(n+1) \\ Charles R Greathouse IV, Nov 05 2017
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CROSSREFS
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Cf. A005117, A073249, A073248, A007675.
Cf. A268331, A268332, A268333, A268334 (squarefrees isolated by more than 2, 3, etc.).
Sequence in context: A249566 A205646 A281192 * A133347 A096990 A175384
Adjacent sequences: A073244 A073245 A073246 * A073248 A073249 A073250
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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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STATUS
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approved
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