The OEIS is supported by the many generous donors to the OEIS Foundation.


(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A247694 Minimal absolute discriminants a(n) of complex quadratic fields with 3-class group of type (3,3), 3-principalization type H.4 (2122), second 3-class group G of even nilpotency class cl(G)=2(n+3), and 3-class tower of unknown length at least 3. 6
21668, 446788, 3843907, 52505588 (list; graph; refs; listen; history; text; internal format)



The 3-principalization type (transfer kernel type, TKT) H.4 (2122) is not a permutation, contains a transposition, and has no fixed point.

The nilpotency condition cl(G)=2n+6 for the second 3-class group is equivalent to a transfer target type, TTT (called IPAD by Boston, Bush and Hajir) of the shape [(3^{n+2},3^{n+3}),(3,3,3),(3,9)^2].

The second 3-class group G is one of two vertices of depth 2 on the coclass tree with root SmallGroup(243,6) contained in the coclass graph G(3,2).

The length of the Hilbert 3-class field tower of all these fields is completely unknown. Therefore, these discriminants are among the foremost challenges of future research, similarly as those of A242873, A247688, A247697.

A247694 is an extremely sparse subsequence of A242878 and it is exceedingly hard to compute a(n) for n>0.

The initial term a(0)=21668 has been recognized as a realization of TKT H.4 in the Dissertation of J. R. Brink(1984). However, Brink did not know that the TKT H.4 can also occur with second 3-class group G=SmallGroup(729,45) of nilpotency class cl(G)=4 and TTT [(3,3,3)^3,(3,9)]. Actually, D. C. Mayer (1991) was the first who proved that the integer 21668 is the smallest term of A247694 and does not belong to A242873.


J. R. Brink, The class field tower for imaginary quadratic number fields of type (3,3), Dissertation, The Ohio State University, 1984.

D. C. Mayer, Principalization in complex S_3 fields, Congressus Numerantium 80 (1991), 73-87. (Proceedings of the Twentieth Manitoba Conference on Numerical Mathematics and Computing, The University of Manitoba, Winnipeg, Manitoba, Canada, 1990.)


Table of n, a(n) for n=0..3.

N. Boston, M. R. Bush and F. Hajir, Heuristics for p-class towers of imaginary quadratic fields, Preprint: arXiv:1111.4679v1 [math.NT], 2011, Math. Ann. (2013).

M. R. Bush and D. C. Mayer, 3-class field towers of exact length 3, Preprint: arXiv:1312.0251v1 [math.NT], 2013.

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

D. C. Mayer, Transfers of metabelian p-groups, Monatsh. Math. 166 (3-4) (2012), 467-495.

D. C. Mayer, Transfers of metabelian p-groups, arXiv:1403.3896 [math.GR], 2014.

D. C. Mayer, The distribution of second p-class groups on coclass graphs, J. Théor. Nombres Bordeaux 25 (2) (2013), 401-456.

D. C. Mayer, The distribution of second p-class groups on coclass graphs, arXiv:1403.3833 [math.NT], 2014.

D. C. Mayer, Principalization algorithm via class group structure, Preprint: arXiv:1403.3839v1 [math.NT], 2014.

Daniel C. Mayer, Periodic sequences of p-class tower groups, arXiv:1504.00851 [math.NT], 2015.

Wikipedia, Artin transfer (group theory), Table 2


For a(0)=21668, we have the ground state of TKT H.4 with TTT [(9,27),(3,3,3),(3,9)^2] and cl(G)=6.

For a(1)=446788, we have the first excited state of TKT H.4 with TTT [(27,81),(3,3,3),(3,9)^2] and cl(G)=8.

a(0) and a(1) are due to D. C. Mayer (2012).

a(2) and a(3) are due to N. Boston, M. R. Bush and F. Hajir (2013).


Cf. A242862, A242863, A242878 (supersequences), A247692, A247693, A247695, A247696, A247697 (disjoint sequences).

Sequence in context: A271021 A262818 A213870 * A309964 A235219 A232121

Adjacent sequences:  A247691 A247692 A247693 * A247695 A247696 A247697




Daniel Constantin Mayer, Oct 12 2014



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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 5 05:10 EDT 2022. Contains 357252 sequences. (Running on oeis4.)