A191408 - OEIS

A191408

Duplicate of A006641.

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, 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, 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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,6

COMMENTS

Same as A006641. - Georg Fischer, Oct 12 2018

LINKS

Table of n, a(n) for n=1..94.

FORMULA

Class number of A003657(n).

MATHEMATICA

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 *);

NumberFieldClassNumber@ Sqrt@ # & /@ Select[-Range@ 300, FundamentalDiscriminantQ]

PROG

(PARI) for(n=1, 300, if(isfundamental(-n), print1(quadclassunit(-n).no, ", "))) \\ Andrew Howroyd, Jul 23 2018

CROSSREFS

Cf. A191410.

Sequence in context: A339765 A268835 A006641 * A115756 A067731 A147844

Adjacent sequences: A191405 A191406 A191407 * A191409 A191410 A191411

KEYWORD

dead

AUTHOR

Robert G. Wilson v, Jun 01 2011

EXTENSIONS

Terms corrected by Andrew Howroyd and Robert G. Wilson v, Jul 24 2018

STATUS

approved