%I #52 Feb 28 2023 11:22:41

%S 18,50,54,90,98,126,150,162,198,234,242,250,270,294,306,338,342,350,

%T 378,414,450,486,490,522,550,558,578,594,630,650,666,686,702,722,726,

%U 738,750,774,810,846,850,882,918,950,954,990,1014,1026,1050,1058,1062,1078,1098,1134,1150

%N Nonsquarefree numbers of the form 4*k + 2.

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

%C From _Peter Munn_, Jan 20 2022: (Start)

%C Even numbers whose square part is odd (and nontrivial).

%C If m is in the sequence then every odd multiple of m is in the sequence.

%C Closed under the operation A059896(.,.).

%C (End)

%H Amiram Eldar, <a href="/A258211/b258211.txt">Table of n, a(n) for n = 1..10000</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/SquarePart.html">Square Part</a>.

%F a(n) = 2*A053850(n). - _Charles R Greathouse IV_, May 26 2015

%e 18 is in this sequence because 4 * 4 + 2 = 18 = 2 * 3^2.

%p remove(numtheory:-issqrfree, [4*i+2 $ i=0..1000]); # _Robert Israel_, May 27 2015

%t Select [Range[300], ! SquareFreeQ[(4 # - 2)] &] 4 - 2 (* _Vincenzo Librandi_, May 24 2015 *)

%o (Magma) [n*4+2: n in [1..300] | not IsSquarefree(4*n+2)];

%o (PARI) select(n->!issquarefree(n), vector(50,n,2*n+9))*2 \\ _Charles R Greathouse IV_, May 26 2015

%Y Intersection of A016825 and either A013929 or A335437.

%Y Cf. A039956, A053850, A059896, A190357.

%K nonn,easy

%O 1,1

%A _Juri-Stepan Gerasimov_, May 23 2015