A138610 - OEIS

%I #22 Aug 27 2024 17:17:48

%S 27,63,75,99,135,147,171,175,207,243,275,279,315,343,351,363,375,387,

%T 423,459,475,495,507,531,539,567,575,603,639,675,711,735,747,775,783,

%U 819,847,855,867,875,891,927,931,963,975,999,1035,1071,1075,1083,1107

%N Nonsquarefree numbers congruent to 3 mod 4.

%C Or, terms in A004767 but not in A039957.

%C The asymptotic density of this sequence is 1/4 - 2/Pi^2 = 0.047357... (A190357) - _Amiram Eldar_, Feb 10 2021

%H Robert Israel, <a href="/A138610/b138610.txt">Table of n, a(n) for n = 1..10000</a>

%F A013929 INTERSECT A004767.

%p remove(numtheory:-issqrfree, [seq(i,i=3..1200,4)]); # _Robert Israel_, Dec 18 2019

%t <<NumberTheory`NumberTheoryFunctions` Select[Range[3,2000,4],SquareFreeQ[ # ]==False&]

%t Select[Range[3,1200,4],!SquareFreeQ[#]&] (* _Harvey P. Dale_, Aug 27 2024 *)

%o (Magma) [4*n+3: n in [0..280] | not IsSquarefree(4*n+3)];  // _Bruno Berselli_, Mar 04 2011

%Y Cf. A004767, A013929, A039957, A190357.

%K nonn

%O 1,1

%A _Zak Seidov_, May 14 2008