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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-François 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. A268331, A268332, A268333, A268334 (squarefrees isolated by more than 2, 3, etc.).
Sequence in context: A249566 A205646 A281192 * A133347 A096990 A175384
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jul 22 2002
STATUS
approved

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Last modified March 28 10:55 EDT 2024. Contains 371241 sequences. (Running on oeis4.)