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A005474 Class numbers of the real quadratic fields Q(sqrt(A005473(n))).

%I A005474 M2215 #25 Jul 08 2025 16:31:13
%S A005474 1,1,1,1,1,3,1,3,5,3,3,7,3,5,7,3,3,5,9,7,3,5,5,15,9,19,5,13,9,9,5,19,
%T A005474 9,5,7,15,13,9,9,15,25,13,9,27,19,15,21,7,13,11,23,9,13,13,11,33,15,
%U A005474 25,23,15,13,29,21,17,43,35,27,33,17,17,27,45,11,63,15,31,17,15,33,15,31,31
%N A005474 Class numbers of the real quadratic fields Q(sqrt(A005473(n))).
%D A005474 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A005474 Robin Visser, <a href="/A005474/b005474.txt">Table of n, a(n) for n = 1..10000</a>
%H A005474 D. Shanks, <a href="http://dx.doi.org/10.1090/S0025-5718-1974-0352049-8">The simplest cubic fields</a>, Math. Comp., 28 (1974), 1137-1152 (see Table 2 page 1143).
%H A005474 <a href="/index/Qua#quadfield">Index entries for sequences related to quadratic fields</a>
%o A005474 (Sage)
%o A005474 def a(n):
%o A005474     m, k = 1, 1
%o A005474     while (m < n): k += 1; m += (k^2+4).is_prime()
%o A005474     return QuadraticField(k^2+4).class_number()  # _Robin Visser_, Dec 07 2024
%Y A005474 Cf. A005472, A005473.
%K A005474 nonn
%O A005474 1,6
%A A005474 _N. J. A. Sloane_
%E A005474 More terms and name edited by _Robin Visser_, Dec 07 2024