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 A328412 Number of solutions to (Z/mZ)* = C_2 X C_(2n), where (Z/mZ)* is the multiplicative group of integers modulo m. 7
 2, 4, 4, 1, 3, 7, 0, 4, 4, 5, 3, 0, 0, 3, 7, 1, 0, 7, 0, 3, 6, 2, 3, 4, 0, 3, 1, 0, 3, 11, 0, 1, 7, 0, 3, 3, 0, 0, 3, 2, 3, 8, 0, 3, 4, 2, 0, 3, 0, 6, 3, 0, 3, 5, 5, 3, 0, 2, 0, 4, 0, 0, 3, 1, 3, 4, 0, 3, 7, 4, 0, 4, 0, 3, 3, 0, 0, 12, 0, 0, 4, 2, 3, 0, 0, 3, 4, 2, 3, 9, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS It is sufficient to check all numbers in the range [A049283(4n), A057635(4n)] for m if 4n is a totient number. Conjecture: every number occurs in this sequence. That is to say, A328416(n) > 0 for every n. Conjecture: this sequence is unbounded. That is to say, A328417 and A328418 are infinite. LINKS Jianing Song, Table of n, a(n) for n = 1..10000 Jianing Song, Solutions to (Z/mZ)* = C_2 X C_(2n), n <= 5000 Wikipedia, Multiplicative group of integers modulo n EXAMPLE See the a-file for the solutions to (Z/mZ)* = C_2 X C_(2n) for n <= 5000. PROG (PARI) a(n) = my(i=0, r=4*n, N=floor(exp(Euler)*r*log(log(r^2))+2.5*r/log(log(r^2)))); for(k=r+1, N, if(eulerphi(k)==r && lcm(znstar(k))==r/2, i++)); i CROSSREFS Cf. A328413 (numbers k such that a(k) > 0), A328414 (indices of 0), A328415 (indices of 1). Cf. A328416 (smallest k such that a(k) = n). Cf. A328417, A328418 (records in this sequence). Cf. also A049823, A057635. Sequence in context: A159778 A243278 A307059 * A079536 A058923 A107500 Adjacent sequences:  A328409 A328410 A328411 * A328413 A328414 A328415 KEYWORD nonn AUTHOR Jianing Song, Oct 14 2019 STATUS approved

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Last modified May 17 22:15 EDT 2021. Contains 343992 sequences. (Running on oeis4.)