A001989 - OEIS

A001989

Class numbers associated with terms of A001988.
(Formerly M3756 N1535)

1, 1, 5, 7, 7, 7, 9, 53, 73, 83, 83, 83, 157, 185, 185, 185, 185, 1927, 2295, 2273, 5313, 5313, 7173, 9529, 18545, 18545, 18545, 18545, 22635, 22635, 66011, 121725, 344909, 344909

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

OFFSET

1,3

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..34.

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]

PROG

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

a(n) = {my(oddpn = prime(n+1)); forprime(p=3, , if (((p%8) == 7) && isok(p, oddpn), return (qfbclassno(-p*if(p%4>1, 4, 1)))); ); } \\ Michel Marcus, Oct 19 2017

CROSSREFS

Cf. A001988.

Sequence in context: A093723 A065773 A114916 * A086056 A154475 A375336

Adjacent sequences: A001986 A001987 A001988 * A001990 A001991 A001992

KEYWORD

nonn

AUTHOR

N. J. A. Sloane

EXTENSIONS

Better name from Sean A. Irvine, Mar 06 2013

Terms corrected by Sean A. Irvine, Mar 06 2013

Offset changed by Michel Marcus, Oct 19 2017

STATUS

approved