A167169 - OEIS

A167169

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.

1, 3, 7, 36, 1131

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OFFSET

0,2

LINKS

EXAMPLE

a(1)=3 since Q[X]/(X^2-z) ramifies only at 2 iff z= -1, 2, -2 (up to squares).

CROSSREFS

KEYWORD

nonn

AUTHOR

STATUS

approved