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 A011796 Number of irreducible alternating Euler sums of depth 6 and weight 6+2n. 4
 1, 3, 9, 20, 42, 75, 132, 212, 333, 497, 728, 1026, 1428, 1932, 2583, 3384, 4389, 5598, 7084, 8844, 10962, 13442, 16380, 19776, 23751, 28301, 33561, 39536, 46376, 54081, 62832, 72624, 83655, 95931, 109668, 124866, 141778, 160398 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(n-6) is the number of aperiodic necklaces (Lyndon words) with 6 black beads and n-6 white beads. REFERENCES J. M. Borwein, D. H. Bailey and R. Girgensohn, Experimentation in Mathematics, A K Peters, Ltd., Natick, MA, 2004. x+357 pp. See p. 147. LINKS D. J. Broadhurst, On the enumeration of irreducible k-fold Euler sums and their roles in knot theory and field theory, arXiv:hep-th/9604128, 1996. FORMULA G.f.: x*(1+x+2*x^2+2*x^3+3*x^4+2*x^6+x^7)/((1-x)^2*(1-x^2)^2*(1-x^3)*(1-x^6)). G.f.: (1/(1-x)^6-1/(1-x^2)^3-1/(1-x^3)^2+1/(1-x^6))/6. - Herbert Kociemba, Oct 23 2016 a(n) = T(n,6), array T as in A051168. MAPLE a:= n-> (Matrix([[42, 20, 9, 3, 1, 0\$7, -1, -4, -9]]). Matrix(15, (i, j)-> if (i=j-1) then 1 elif j=1 then [2, 1, -3, -1, 1, 4, -3, -3, 4, 1, -1, -3, 1, 2, -1][i] else 0 fi)^(n-5))[1, 1]: seq(a(n), n=1..50); # Alois P. Heinz, Aug 04 2008 MATHEMATICA a[n_] := Sum[Binomial[(n+6)/d, 6/d]*MoebiusMu[d], {d, Divisors[GCD[6, n+6]]}]/(n+6); Array[a, 40] (* Jean-François Alcover, Feb 02 2015 *) CROSSREFS Cf. A000031, A001037, A051168. Sequence in context: A192951 A027114 A145070 * A164680 A210634 A295148 Adjacent sequences:  A011793 A011794 A011795 * A011797 A011798 A011799 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified October 22 21:09 EDT 2018. Contains 316505 sequences. (Running on oeis4.)