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 A138610 #22 Aug 27 2024 17:17:48 %S A138610 27,63,75,99,135,147,171,175,207,243,275,279,315,343,351,363,375,387, %T A138610 423,459,475,495,507,531,539,567,575,603,639,675,711,735,747,775,783, %U A138610 819,847,855,867,875,891,927,931,963,975,999,1035,1071,1075,1083,1107 %N A138610 Nonsquarefree numbers congruent to 3 mod 4. %C A138610 Or, terms in A004767 but not in A039957. %C A138610 The asymptotic density of this sequence is 1/4 - 2/Pi^2 = 0.047357... (A190357) - _Amiram Eldar_, Feb 10 2021 %H A138610 Robert Israel, <a href="/A138610/b138610.txt">Table of n, a(n) for n = 1..10000</a> %F A138610 A013929 INTERSECT A004767. %p A138610 remove(numtheory:-issqrfree, [seq(i,i=3..1200,4)]); # _Robert Israel_, Dec 18 2019 %t A138610 <<NumberTheory`NumberTheoryFunctions` Select[Range[3,2000,4],SquareFreeQ[ # ]==False&] %t A138610 Select[Range[3,1200,4],!SquareFreeQ[#]&] (* _Harvey P. Dale_, Aug 27 2024 *) %o A138610 (Magma) [4*n+3: n in [0..280] | not IsSquarefree(4*n+3)]; // _Bruno Berselli_, Mar 04 2011 %Y A138610 Cf. A004767, A013929, A039957, A190357. %K A138610 nonn %O A138610 1,1 %A A138610 _Zak Seidov_, May 14 2008