A001989 Class numbers associated with terms of A001988.

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

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn

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

• 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]

Crossrefs

Cf. A001988.

Programs

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

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