login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A283658 Numbers d > 1 such that the class number of Q(sqrt(d)) is strictly greater than the class number of Q(sqrt(m)) for all m < d. 1
10, 79, 82, 226, 730, 1534, 2305, 3601, 4762, 5626, 11026, 21610, 23410, 27226, 38026, 50626, 116554, 164026, 176401, 189226, 342226, 345745, 411394, 518401, 540226, 613090, 804610, 893026, 1071226 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Every element d of the sequence is squarefree because, if f is the squarefree part of d, then Q(sqrt(f)) = Q(sqrt(d)). If f would be < d, the class number of Q(sqrt(f)) would not be < the class number of Q(sqrt(d)). Thus, f = d.

REFERENCES

Z. I. Borevich and I. R. Shafarevich, Number Theory. Academic Press, NY, 1966.

LINKS

Table of n, a(n) for n=1..29.

EXAMPLE

The sequence starts with 10 because the class number of Q(sqrt(10)) = 2 and all fields Q(sqrt(m)) with m < 10 have class number 1.

The next term is 79 because the class number of Q(sqrt(79)) is 3 and all fields Q(sqrt(m)) with m < 79 have class number 1 or 2.

MATHEMATICA

A={}; hx = 1; d = 2; While[hx<300, d++; If[SquareFreeQ[d], h = NumberFieldClassNumber[Sqrt[d]]; If[h > hx, AppendTo[A, d]; hx = h]]]; A

PROG

(PARI) classn(n) = qfbclassno(if(n%4>1, 4, 1)*n);

isok(d) = {if (issquarefree(d), cld = classn(d); for (k=2, d-1, if (issquarefree(k) && (classn(k) >= cld), return (0))); 1; ); } \\ Michel Marcus, Mar 13 2017

CROSSREFS

Cf. A003172, A003649, A283659.

Sequence in context: A056986 A243247 A222701 * A160655 A006469 A288630

Adjacent sequences:  A283655 A283656 A283657 * A283659 A283660 A283661

KEYWORD

nonn,more

AUTHOR

Emmanuel Vantieghem, Mar 13 2017

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 18 15:04 EDT 2019. Contains 322209 sequences. (Running on oeis4.)