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%I #16 Feb 01 2026 10:03:23
%S 160,408,552,1186,848,1600,975,2754,1804,2484,1348,4908,1533,2744,
%T 3764,6660,1820,5191,1916,7423,4617,3882,2347,13130,4129
%N a(n) is the number of imaginary biquadratic fields with class number 2*n.
%C There are finitely many imaginary biquadratic fields given a class number.
%H J. M. Basilla and I. A. C. Fajardo, <a href="https://doi.org/10.3792/pjaa.102.001">Imaginary biquadratic number fields with small odd class numbers</a>, Proc. Japan Acad. Ser. A Math. Sci. 102(1) (2026), 1-6.
%H D. A. Buell, H. C. Williams and K. S. Williams, <a href="https://doi.org/10.2307/2006137">On the imaginary bicyclic biquadratic fields with class-number 2</a>, Math. Comp. 31(140) (1977), 1034-1042.
%e There are a(1) = 160 imaginary biquadratic fields with class number 2.
%e There are a(2) = 408 imaginary biquadratic fields with class number 4.
%Y Cf. A159456, A378956.
%K nonn,more
%O 1,1
%A _Iana Angela C. Fajardo_, Jan 27 2026