OFFSET
1,2
COMMENTS
A subset of the nonprime numbers (A018252).
Positive fundamental discriminants (A003658) that are not Pythagorean primes (A002144). - Paul Muljadi, Mar 30 2008
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
a(n) appears to be asymptotic to C*n with C = 3.91... .
MATHEMATICA
FundamentalDiscriminantQ[d_] := Module[{m, mod = Mod[d, 4]}, If[mod > 1, Return[False]]; If[mod == 1, Return[ SquareFreeQ[d] && d != 1]]; m = d/4; Return[ SquareFreeQ[m] && Mod[m, 4] > 1]]; Join[{1}, Select[ Range[270], !PrimeQ[#] && FundamentalDiscriminantQ[#]& ]] (* Jean-François Alcover, Jun 05 2012, after Eric W. Weisstein *)
PROG
(PARI) isok(m) = !isprime(m) && (quaddisc(m) == m); \\ Michel Marcus, Feb 18 2021
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Aug 10 2002
STATUS
approved