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 A091728 Number of prime ideals of Z[sqrt(-5)] of norm n. 3
 0, 1, 2, 0, 1, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 2, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 2, 0, 0, 0, 2, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS It follows that the total number of ideals of norm n is A035170(n). REFERENCES David A. Cox, Primes of the form x^2+ny^2, Wiley, 1989. A. Frohlich and M. J. Taylor, Algebraic number theory, Cambridge university press, 1991. LINKS Antti Karttunen, Table of n, a(n) for n = 1..65537 FORMULA a(n)=0 if n is not in A091727. If n is in A091727 and n is 2, 5 or a square then a(n)=1. Otherwise a(n)=2. PROG (PARI) isA091727(n) = { my(ms = [1, 2, 3, 5, 7, 9], p, e=isprimepower(n, &p)); if(!e || e>2, 0, bitxor(e-1, !!vecsearch(ms, p%20))); }; A091728(n) = if(!isA091727(n), 0, (2-((2==n)||(5==n)||issquare(n)))); \\ Antti Karttunen, Feb 24 2020 CROSSREFS Cf. A035170, A091727. Sequence in context: A357293 A357119 A357883 * A108069 A227837 A263099 Adjacent sequences: A091725 A091726 A091727 * A091729 A091730 A091731 KEYWORD easy,nonn AUTHOR Paul Boddington, Feb 02 2004 EXTENSIONS Data section extended up to a(121) by Antti Karttunen, Feb 24 2020 STATUS approved

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Last modified June 23 08:01 EDT 2024. Contains 373629 sequences. (Running on oeis4.)