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 A191408 #24 Oct 14 2018 12:15:20 %S A191408 1,1,1,1,1,2,1,2,3,2,3,2,4,2,1,5,2,2,4,4,3,1,4,7,5,3,4,6,2,2,8,5,6,3, %T A191408 8,2,6,10,4,2,5,5,4,4,3,10,2,7,6,4,10,1,8,11,4,5,8,4,2,13,4,9,4,3,6, %U A191408 14,4,7,5,4,12,2,2,15,6,6,8,7,12,4,8,13,8,2,11,8,4,3,14,4,4,8,10,8 %N A191408 Duplicate of A006641. %C A191408 Same as A006641. - _Georg Fischer_, Oct 12 2018 %F A191408 Class number of A003657(n). %t A191408 FundamentalDiscriminantQ[n_Integer] := n != 1 && (Mod[n, 4] == 1 || !Unequal[ Mod[n, 16], 8, 12]) && SquareFreeQ[n/2^IntegerExponent[n, 2]] (* via _Eric W. Weisstein_ *); %t A191408 NumberFieldClassNumber@ Sqrt@ # & /@ Select[-Range@ 300, FundamentalDiscriminantQ] %o A191408 (PARI) for(n=1, 300, if(isfundamental(-n), print1(quadclassunit(-n).no, ", "))) \\ _Andrew Howroyd_, Jul 23 2018 %Y A191408 Cf. A191410. %K A191408 dead %O A191408 1,6 %A A191408 _Robert G. Wilson v_, Jun 01 2011 %E A191408 Terms corrected by _Andrew Howroyd_ and _Robert G. Wilson v_, Jul 24 2018