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%I #19 Mar 08 2021 02:47:17
%S 3,12,21,27,30,39,48,57,66,75,84,93,102,108,111,120,129,138,147,156,
%T 165,174,183,189,192,201,210,219,228,237,243,246,255,264,270,273,282,
%U 291,300,309,318,327,336,345,351,354,363,372,381,390,399
%N Numbers of the form 3^(2i+1)*(3*j+1).
%C The numbers not of the form x^2+y^2+6z^2.
%C Numbers whose squarefree part is congruent to 3 modulo 9. Compare with A329575. - _Peter Munn_, May 17 2020
%C The asymptotic density of this sequence is 1/8. - _Amiram Eldar_, Mar 08 2021
%H Amiram Eldar, <a href="/A055041/b055041.txt">Table of n, a(n) for n = 1..10000</a>
%H L. J. Mordell, <a href="https://doi.org/10.1093/qmath/os-1.1.276">A new Waring's problem with squares of linear forms</a>, Quart. J. Math., 1 (1930), 276-288 (see p. 283).
%F a(n) = A055047(n) * 3. - _Peter Munn_, May 17 2020
%t f[p_, e_] := (p^Mod[e, 2]); sqfpart[n_] := Times @@ f @@@ FactorInteger[n]; Select[Range[400], Mod[sqfpart[#], 9] == 3 &] (* _Amiram Eldar_, Mar 08 2021 *)
%Y Intersection of A145204 and A189716.
%Y Complement of A055040 with respect to A145204\{0}.
%Y Complement of A055048 with respect to A189716.
%Y Cf. A007913, A055047, A329575.
%K nonn
%O 1,1
%A _N. J. A. Sloane_, Jun 01 2000
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