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 A001989 Class numbers associated with entries of A001988. (Formerly M3756 N1535) 0
 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 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 A264527 Adjacent sequences:  A001986 A001987 A001988 * A001990 A001991 A001992 KEYWORD nonn AUTHOR 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

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Last modified December 12 15:11 EST 2019. Contains 329960 sequences. (Running on oeis4.)