This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A072901 #18 Nov 26 2013 12:02:36 %S A072901 6,10,14,15,22,26,30,34,35,38,39,42,46,51,55,58,62,66,70,74,78,82,86, %T A072901 87,91,94,95,102,106,110,111,114,115,118,119,122,123,130,134,138,142, %U A072901 143,146,154,155,158,159,166,170,174,178,182,183,186,187,190,194,195 %N A072901 Composite numbers n such that the discriminant of the quadratic field Q(sqrt(n)) equals 4n. %C A072901 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 A072901 If prime numbers were accepted, then sequence A230375 would have been obtained. - _Michel Marcus_, Nov 26 2013 %H A072901 Wikipedia, <a href="http://en.wikipedia.org/wiki/Quadratic_field">Quadratic field</a> %o A072901 (PARI) isok(n) = !isprime(n) && (quaddisc(n) == 4*n); \\ _Michel Marcus_, Nov 26 2013 %Y A072901 Cf. A037449. %K A072901 easy,nonn %O A072901 1,1 %A A072901 _Benoit Cloitre_, Aug 10 2002