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 A306598 Determinant of the circulant matrix whose first column corresponds to the divisors of n. 1
 1, -3, -8, 49, -24, -960, -48, -3375, 676, -8640, -120, -2247392, -168, -34560, -46080, 923521, -288, -28789488, -360, -54867456, -184320, -216000, -528, -89384770560, 15376, -423360, -512000, -438939648, -840, -558786571200, -960, -992436543, -1152000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS From Robert Israel, Mar 06 2019: a(n) is divisible by A000203(n). If n is not a square, a(n) is divisible by A000203(n)*A071324(n). (End) LINKS Robert Israel, Table of n, a(n) for n = 1..10000 Wikipedia, Circulant matrix FORMULA Apparently, a(n) > 0 iff n is a square. a(p) = p^2 - 1 for any prime number p. a(p^2) = p^6 - 2*p^3 + 1 for any prime number p. a(2^k) = A086459(k+1) for any k >= 0. If p < q are primes, a(p*q) = -(p^4-1)*(q^2-1)^2. - Robert Israel, Mar 06 2019 EXAMPLE For n = 12: - the divisors of 12 are: 1, 2, 3, 4, 6, 12, - the corresponding circulant matrix is:     [ 1 12  6  4  3  2]     [ 2  1 12  6  4  3]     [ 3  2  1 12  6  4]     [ 4  3  2  1 12  6]     [ 6  4  3  2  1 12]     [12  6  4  3  2  1] - its determinant is -2247392, - hence, a(12) = -2247392. MAPLE f:= proc(n) local F, d; uses numtheory, LinearAlgebra;   F:= sort(convert(divisors(n), list));   d:= nops(F);   Determinant(Matrix(d, d, shape=Circulant[F])) end proc: map(f, [\$1..100]); # Robert Israel, Mar 06 2019 MATHEMATICA a[n_] := Module[{dd = Divisors[n], m, r}, m = Length[dd]; r = E^(2 Pi I/m); Product[Sum[dd[[j+1]] r^(j k), {j, 0, m-1}], {k, 0, m-1}] // FullSimplify]; Array[a, 100] (* Jean-François Alcover, Oct 17 2020 *) PROG (PARI) a(n) = my (d=divisors(n)); my (m=matrix(#d, #d, i, j, d[1+(i-j)%#d])); return (matdet(m)) CROSSREFS Cf. A027750, A086459, A177894. Sequence in context: A003216 A146161 A304698 * A019015 A305217 A316797 Adjacent sequences:  A306595 A306596 A306597 * A306599 A306600 A306601 KEYWORD sign,look AUTHOR Rémy Sigrist, Feb 27 2019 STATUS approved

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Last modified May 11 18:21 EDT 2021. Contains 343808 sequences. (Running on oeis4.)