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%I #16 May 13 2013 01:54:04
%S 82,130,145,170,195,210,219,231,255,274,290,291,322,323,330,370,390,
%T 410,434,435,438,445,455,462,483,505,510,514,530,546,555,570,579,582,
%U 595,610,615,626,627,651,658,663,674,689,690,706,714,715,723,731,754,759,770
%N Q(sqrt(n)) has class number 4.
%H Charles R Greathouse IV, <a href="/A029704/b029704.txt">Table of n, a(n) for n = 1..10000</a>
%H <a href="/index/Qua#quadfield">Index entries for sequences related to quadratic fields</a>
%t Select[Range[770], SquareFreeQ[#] && NumberFieldClassNumber@Sqrt[#] == 4 &] (* _Arkadiusz Wesolowski_, Oct 18 2012 *)
%o (PARI) is(n)=if(issquarefree(n), my(c=bnfinit('x^2-n).cyc); c==[4] || c==[2,2], 0) \\ _Charles R Greathouse IV_, Oct 18 2012
%Y Cf. A003172, A029702-A029703, A029705, A218038-A218042.
%K nonn
%O 1,1
%A Paolo Dominici (pl.dm(AT)libero.it)
%E Initial term added by _Arkadiusz Wesolowski_, Oct 18 2012
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