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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A094613 Fundamental discriminants of real quadratic number fields with class number 4. 4
145, 328, 445, 505, 520, 680, 689, 777, 780, 793, 840, 876, 897, 901, 905, 924, 1020, 1045, 1096, 1105, 1145, 1160, 1164, 1221, 1288, 1292, 1313, 1320, 1365, 1480, 1560, 1640, 1677, 1736, 1740, 1745, 1752, 1820, 1848, 1885, 1932, 2005, 2040, 2056, 2120, 2145 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..1000

Eric Weisstein's World of Mathematics, Class Number

Index entries for sequences related to quadratic fields

MATHEMATICA

Select[Range[2145], NumberFieldDiscriminant@Sqrt[#] == # && NumberFieldClassNumber@Sqrt[#] == 4 &] (* Arkadiusz Wesolowski, Oct 22 2012 *)

PROG

(PARI) {ok(n) = n>10 && isfundamental(n) && qfbclassno(n)==4};

for(n=1, 2500, if(ok(n)==1, print1(n, ", "))) \\ G. C. Greubel, Mar 01 2019

(Sage)

is_fund_and_qfbcn_1 = lambda n: is_fundamental_discriminant(n) and QuadraticField(n, 'a').class_number() == 4;

A094613 = lambda n: filter(is_fund_and_qfbcn_1, (1, 2, .., n));

A094613(2500) # G. C. Greubel, Mar 01 2019

CROSSREFS

Cf. A003656, A094619, A094612, A094614, A218156-A218160.

Sequence in context: A177223 A318530 A158133 * A207058 A116208 A211470

Adjacent sequences:  A094610 A094611 A094612 * A094614 A094615 A094616

KEYWORD

nonn

AUTHOR

Eric W. Weisstein, May 14 2004

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 September 18 02:20 EDT 2019. Contains 327149 sequences. (Running on oeis4.)