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 A001991 Class numbers associated with entries of A001990. (Formerly M0212 N0863) 0
 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 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] 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 A147793 A052298 Adjacent sequences:  A001988 A001989 A001990 * A001992 A001993 A001994 KEYWORD nonn,more AUTHOR EXTENSIONS Better name from Sean A. Irvine, Mar 06 2013 Offset changed by Michel Marcus, Oct 19 2017 STATUS approved

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Last modified December 6 14:15 EST 2019. Contains 329806 sequences. (Running on oeis4.)