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%I #6 Mar 31 2012 23:00:50
%S 1,3,7,36,1131
%N a(n) is the number of isomorphism classes of iterated quadratic extensions of the field of rationals of degree 2^n that ramify only at 2.
%e a(1)=3 since Q[X]/(X^2-z) ramifies only at 2 iff z= -1, 2, -2 (up to squares).
%K nonn
%O 0,2
%A _Gaël Collinet_, Oct 29 2009
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