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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. 0
1, 3, 7, 36, 1131 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..4.

EXAMPLE

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

CROSSREFS

Sequence in context: A081010 A100377 A270396 * A269995 A281093 A199347

Adjacent sequences:  A167166 A167167 A167168 * A167170 A167171 A167172

KEYWORD

nonn

AUTHOR

Gaël Collinet, Oct 29 2009

STATUS

approved

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Last modified May 16 06:54 EDT 2021. Contains 343939 sequences. (Running on oeis4.)