A072901 - OEIS

%I #18 Nov 26 2013 12:02:36

%S 6,10,14,15,22,26,30,34,35,38,39,42,46,51,55,58,62,66,70,74,78,82,86,

%T 87,91,94,95,102,106,110,111,114,115,118,119,122,123,130,134,138,142,

%U 143,146,154,155,158,159,166,170,174,178,182,183,186,187,190,194,195

%N Composite numbers n such that the discriminant of the quadratic field Q(sqrt(n)) equals 4n.

%C Conjecture: All terms are squarefree. Example: 6=2*3; 15=3*5; 30=2*3*5; 154=2*7*11; 195=3*5*13. - _Vincenzo Librandi_, Aug 08 2010 and _Michel Marcus_, Nov 26 2013

%C If prime numbers were accepted, then sequence A230375 would have been obtained. - _Michel Marcus_, Nov 26 2013

%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Quadratic_field">Quadratic field</a>

%o (PARI) isok(n) = !isprime(n) && (quaddisc(n) == 4*n); \\ _Michel Marcus_, Nov 26 2013

%Y Cf. A037449.

%K easy,nonn

%O 1,1

%A _Benoit Cloitre_, Aug 10 2002