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A073247 Squarefree numbers n such that n-1 and n+1 are not squarefree. 10
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Probably 11*n < a(n) < 12*n for n > 189. - Charles R Greathouse IV, Nov 05 2017

LINKS

Christopher E. Thompson, Table of n, a(n) for n = 1..10000

MAPLE

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

MATHEMATICA

Reap[For[n = 0, n <= 1000, n++, If[SquareFreeQ[n] && !SquareFreeQ[n-1] && !SquareFreeQ[n+1], Sow[n]]]][[2, 1]] (* Jean-Fran├žois Alcover, Feb 26 2019 *)

PROG

(PARI) is(n)=!issquarefree(n-1) && issquarefree(n) && !issquarefree(n+1) \\ Charles R Greathouse IV, Nov 05 2017

CROSSREFS

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

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Jul 22 2002

STATUS

approved

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Last modified January 23 22:16 EST 2020. Contains 331177 sequences. (Running on oeis4.)