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 A208596 Number of n-bead necklaces labeled with numbers -7..7 not allowing reversal, with sum zero. 2
 1, 8, 57, 568, 6077, 69784, 833253, 10259448, 129245091, 1658145128, 21589248803, 284548542120, 3789094334455, 50900085245304, 688944374917247, 9386664978851448, 128633790260673263, 1771859642698543096, 24518513933529549357, 340679786167936420216 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Andrew Howroyd, Table of n, a(n) for n = 1..100 FORMULA a(n) = (1/n) * Sum_{d | n} totient(n/d) * A201551(d). - Andrew Howroyd, Mar 02 2017 EXAMPLE Some solutions for n=4: .-4...-7...-7...-7...-4...-3...-3...-5...-2...-5...-7...-6...-6...-7...-6...-7 ..0....4...-1....6....2...-3...-1....1....0...-3....6....3....5....1...-1...-2 ..6....3....2...-1....1...-1...-2....7....1....3...-3...-3....5....7....0....4 .-2....0....6....2....1....7....6...-3....1....5....4....6...-4...-1....7....5 MATHEMATICA comps[r_, m_, k_] := Sum[(-1)^i*Binomial[r - 1 - i*m, k - 1]*Binomial[k, i], {i, 0, Floor[(r - k)/m]}]; a[n_Integer, k_] := DivisorSum[n, EulerPhi[n/#] comps[#*(k + 1), 2 k + 1, #] &]/n; a[n_] = a[n, 7]; Array[a, 20] (* Jean-François Alcover, Nov 01 2017, after Andrew Howroyd *) CROSSREFS Column 7 of A208597. Sequence in context: A199555 A241594 A241595 * A324205 A002402 A015464 Adjacent sequences: A208593 A208594 A208595 * A208597 A208598 A208599 KEYWORD nonn AUTHOR R. H. Hardin, Feb 29 2012 EXTENSIONS a(14)-a(20) from Andrew Howroyd, Mar 02 2017 STATUS approved

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Last modified February 8 12:15 EST 2023. Contains 360138 sequences. (Running on oeis4.)