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%I #48 Jun 11 2020 02:58:24
%S 1,4,7,9,10,13,16,19,22,25,28,31,34,36,37,40,43,46,49,52,55,58,61,63,
%T 64,67,70,73,76,79,81,82,85,88,90,91,94,97,100,103,106,109,112,115,
%U 117,118,121,124,127,130,133,136,139,142,144,145,148,151
%N Numbers of the form 9^i*(3*j+1).
%C The numbers not of the form 2x^2+3y^2+3z^2.
%C Also values of n such that numbers of the form x^2+n*y^2 for some integers x, y cannot have prime factor of 3 raised to an odd power. - _V. Raman_, Dec 18 2013
%C Numbers whose squarefree part is congruent to 1 modulo 3. - _Peter Munn_, May 17 2020
%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) = 8n/3 + O(log n). - _Charles R Greathouse IV_, Dec 19 2013
%F a(n) = A055041(n)/3. - _Peter Munn_, May 17 2020
%o (PARI) is(n)=n/=9^valuation(n,9); n%3==1 \\ _Charles R Greathouse IV_ and _V. Raman_, Dec 19 2013
%Y Intersection of A007417 and A189715.
%Y Complement of A055048 with respect to A007417.
%Y Complement of A055040 with respect to A189715.
%Y Cf. A007913, A055041, A055046, A233998, A233999.
%K nonn
%O 1,2
%A _N. J. A. Sloane_, Jun 01 2000
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