A001991 - OEIS

A001991

Class numbers associated with terms of A001990.
(Formerly M0212 N0863)

2, 2, 2, 2, 2, 2, 2, 2, 46, 46, 46, 46, 46, 46, 406, 718, 950, 950, 950, 1698, 1698, 1698, 1698, 1698, 3990, 3990, 3990, 53510, 77970, 89478, 89478, 89478, 89478, 89478, 89478

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

OFFSET

1,1

REFERENCES

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

Table of n, a(n) for n=1..35.

D. H. Lehmer, E. Lehmer and D. Shanks, Integer sequences having prescribed quadratic character, Math. Comp., 24 (1970), 433-451.

D. H. Lehmer, E. Lehmer and D. Shanks, Integer sequences having prescribed quadratic character, Math. Comp., 24 (1970), 433-451 [Annotated scanned copy]

Index entries for sequences related to quadratic fields

FORMULA

a(n) = ClassNumber(-8*A001990(n)). - Sean A. Irvine, Mar 06 2013

PROG

(PARI) isok(p, oddpn) = {forprime(q=3, oddpn, if (kronecker(p, q) != -kronecker(-2, q), return (0)); ); return (1); }

a(n) = {oddpn = prime(n+1); forprime(p=3, , if (((p%8) == 5) && isok(p, oddpn), return (qfbclassno(-8*p))); ); } \\ Michel Marcus, Oct 19 2017

CROSSREFS

Cf. A001990.

Sequence in context: A171818 A248777 A175101 * A305706 A359309 A147793

Adjacent sequences: A001988 A001989 A001990 * A001992 A001993 A001994

KEYWORD

nonn,more