The OEIS is supported by the many generous donors to the OEIS Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A250238 Fundamental discriminants d uniquely characterizing all complex biquadratic fields Q(sqrt(-3),sqrt(d)) which have 3-class group of type (3,3) and second 3-class group isomorphic to SmallGroup(81,9). 7
 469, 1489, 1708, 1937, 2557, 2941, 2981, 3021, 3173, 3305, 3580, 3592, 3736 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For the discriminants d in A250238, the 3-class field tower of K=Q(sqrt(-3),sqrt(d)) has exactly two stages and the second 3-class group G of K is given by the metabelian 3-group G=SmallGroup(81,9) with transfer kernel type a.1, (0,0,0,0), transfer target type [(3,9),(3,3)^3] and coclass 1. Actually, this is the ground state on the coclass-1 graph. The reason the 3-class field tower of K must stop at the second Hilbert 3-class field is Blackburn's Theorem on two-generated 3-groups G whose commutator subgroup G' also has two generators. In fact, the group G=SmallGroup(81,9) has two-generated commutator subgroup G' of type (3,3). REFERENCES H. U. Besche, B. Eick, and E. A. O'Brien, The SmallGroups Library - a Library of Groups of Small Order, 2005, an accepted and refereed GAP 4 package, available also in MAGMA. LINKS Table of n, a(n) for n=1..13. N. Blackburn, On prime-power groups in which the derived group has two generators, Proc. Camb. Phil. Soc. 53 (1957), 19-27. D. C. Mayer, The second p-class group of a number field, Int. J. Number Theory 8 (2) (2012), 471-505. D. C. Mayer, The second p-class group of a number field. Preprint: arXiv:1403.3899v1 [math.NT], 2014. D. C. Mayer, Principalization algorithm via class group structure, Preprint: arXiv:1403.3839v1 [math.NT], 2014; J. Théor. Nombres Bordeaux 26 (2014), no. 2, 415-464. PROG (Magma)SetClassGroupBounds("GRH"); for n := 469 to 10000 do cnd := false; if (1 eq n mod 4) and IsSquarefree(n) then cnd := true; end if; if (0 eq n mod 4) then r := n div 4; if IsSquarefree(r) and ((2 eq r mod 4) or (3 eq r mod 4)) then cnd := true; end if; end if; if (true eq cnd) then R := QuadraticField(n); E := QuadraticField(-3); K := Compositum(R, E); C, mC := ClassGroup(K); if ([3, 3] eq pPrimaryInvariants(C, 3)) then s := Subgroups(C: Quot := ); a := [AbelianExtension(Inverse(mq)*mC) where _, mq := quo : x in s]; b := [NumberField(x) : x in a]; d := [MaximalOrder(x) : x in a]; b := [AbsoluteField(x) : x in b]; c := [MaximalOrder(x) : x in b]; c := [OptimizedRepresentation(x) : x in b]; b := [NumberField(DefiningPolynomial(x)) : x in c]; a := [Simplify(LLL(MaximalOrder(x))) : x in b]; if IsNormal(b) then H := Compositum(NumberField(a), NumberField(a)); else H := Compositum(NumberField(a), NumberField(a)); end if; O := MaximalOrder(H); CH := ClassGroup(LLL(O)); if ([3, 3] eq pPrimaryInvariants(CH, 3)) then n, ", "; end if; end if; end if; end for; CROSSREFS A006832, A250235, A250236 are supersequences, A250237, A250239, A250240, A250241, A250242 are disjoint sequences. Sequence in context: A205407 A045305 A349275 * A234125 A259423 A188138 Adjacent sequences: A250235 A250236 A250237 * A250239 A250240 A250241 KEYWORD nonn,hard,more AUTHOR Daniel Constantin Mayer, Nov 16 2014 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 21 07:12 EDT 2023. Contains 365494 sequences. (Running on oeis4.)