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 A281192 Numbers with no squarefree neighbors. 3
 17, 19, 26, 49, 51, 53, 55, 89, 91, 97, 99, 125, 127, 149, 151, 161, 163, 170, 197, 199, 233, 235, 241, 243, 244, 249, 251, 269, 271, 293, 295, 305, 307, 337, 339, 341, 343, 349, 351, 362, 377, 379, 413, 415, 424, 449, 451, 476, 485, 487, 489, 491, 521, 523, 530, 549, 551, 557, 559, 577 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Includes all n == 17 or 19 (mod 36), also 2*p^2-1 and 2*p^2+1 for odd primes p. - Robert Israel, Jan 17 2017 This sequence has density around 0.106.... - Charles R Greathouse IV, Jan 23 2017 LINKS Robert Israel, Table of n, a(n) for n = 1..10000 EXAMPLE 17 is in this sequence because 17 - 1 = 16 = 2^4 and 17 + 1 = 18 = 2*3^2 are not squarefree. MAPLE select(t -> not numtheory:-issqrfree(t-1) and not numtheory:-issqrfree(t+1), [\$1..1000]); # Robert Israel, Jan 17 2017 MATHEMATICA Select[Range[600], !SquareFreeQ[# - 1] && !SquareFreeQ[# + 1] &] (* Vincenzo Librandi, Jan 17 2017 *) PROG (MAGMA) [n: n in [2..600] | not IsSquarefree(n-1) and not IsSquarefree(n+1)]; (PARI) is(n)=!issquarefree(n-1) && !issquarefree(n+1) \\ Charles R Greathouse IV, Jan 23 2017 CROSSREFS Supersequence of A075432 and A235578. Cf. A005117, A280892. Sequence in context: A334287 A249566 A205646 * A073247 A133347 A096990 Adjacent sequences:  A281189 A281190 A281191 * A281193 A281194 A281195 KEYWORD nonn,easy AUTHOR Juri-Stepan Gerasimov, Jan 16 2017 STATUS approved

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Last modified September 27 12:30 EDT 2020. Contains 337380 sequences. (Running on oeis4.)