OFFSET
1,1
COMMENTS
Also numbers such that the discriminant of the quadratic field Q(sqrt(n)) equals 4n. - Michel Marcus, Nov 26 2013
The asymptotic density of this sequence is 4/Pi^2 (A185199). - Amiram Eldar, Feb 23 2021
LINKS
Colin Barker, Table of n, a(n) for n = 1..1000
Wikipedia, Quadratic field.
MATHEMATICA
Select[Range[200], SquareFreeQ[#]&&MemberQ[{2, 3}, Mod[#, 4]]&] (* Harvey P. Dale, Feb 04 2015 *)
PROG
(PARI) s=[]; for(n=1, 200, if(issquarefree(n) && n%4!=1, s=concat(s, n))); s
CROSSREFS
KEYWORD
nonn
AUTHOR
Colin Barker, Oct 17 2013
STATUS
approved