This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A281192 #25 Jun 29 2024 18:05:18
%S A281192 17,19,26,49,51,53,55,89,91,97,99,125,127,149,151,161,163,170,197,199,
%T A281192 233,235,241,243,244,249,251,269,271,293,295,305,307,337,339,341,343,
%U A281192 349,351,362,377,379,413,415,424,449,451,476,485,487,489,491,521,523,530,549,551,557,559,577
%N A281192 Numbers with no squarefree neighbors.
%C A281192 Includes all k == 17 or 19 (mod 36), also 2*p^2-1 and 2*p^2+1 for odd primes p. - _Robert Israel_, Jan 17 2017
%C A281192 This sequence has density around 0.106.... - _Charles R Greathouse IV_, Jan 23 2017
%C A281192 More accurately, the asymptotic density of this sequence is 1 - 2/zeta(2) + Product_{p prime} (1 - 2/p^2) = 1 - 2 * A059956 + A065474 = 0.1067798952... - _Amiram Eldar_, Feb 25 2021
%H A281192 Robert Israel, <a href="/A281192/b281192.txt">Table of n, a(n) for n = 1..10000</a>
%e A281192 17 is in this sequence because 17 - 1 = 16 = 2^4 and 17 + 1 = 18 = 2*3^2 are not squarefree.
%p A281192 select(t -> not numtheory:-issqrfree(t-1) and not numtheory:-issqrfree(t+1), [$1..1000]); # _Robert Israel_, Jan 17 2017
%t A281192 Select[Range[600], !SquareFreeQ[# - 1] && !SquareFreeQ[# + 1] &] (* _Vincenzo Librandi_, Jan 17 2017 *)
%o A281192 (Magma) [n: n in [2..600] | not IsSquarefree(n-1) and not IsSquarefree(n+1)];
%o A281192 (PARI) is(n)=!issquarefree(n-1) && !issquarefree(n+1) \\ _Charles R Greathouse IV_, Jan 23 2017
%Y A281192 Supersequence of A075432 and A235578.
%Y A281192 Cf. A005117, A059956, A065474, A280892.
%K A281192 nonn,easy
%O A281192 1,1
%A A281192 _Juri-Stepan Gerasimov_, Jan 16 2017