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 A261496 Number of necklaces with n white beads and n^2-n black beads. 2
 1, 1, 2, 10, 116, 2126, 54132, 1753074, 69159400, 3220837534, 173103115760, 10551652603526, 719578430426044, 54297978110913252, 4492502634679508204, 404469190271900056316, 39370123445405248353744, 4120204305690280446004838, 461365717080849798202175772 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Alois P. Heinz, Table of n, a(n) for n = 0..335 F. Ruskey, Necklaces, Lyndon words, De Bruijn sequences, etc. [Cached copy, with permission, pdf format only] Eric Weisstein's World of Mathematics, Necklace Wikipedia, Necklace (combinatorics) FORMULA a(n) = 1/(n^2) * Sum_{d|n} C(n^2/d,n/d) * A000010(d) for n>0, a(0) = 1. a(n) ~ exp(n-1/2) * n^(n-5/2) / sqrt(2*Pi). - Vaclav Kotesovec, Aug 22 2015 MAPLE with(numtheory): a:= n-> `if`(n=0, 1, add(binomial(n^2/d, n/d)             *phi(d), d=divisors(n))/n^2): seq(a(n), n=0..20); CROSSREFS Lower diagonal of A261494. Cf. A000010. Sequence in context: A132522 A187653 A131811 * A006121 A110951 A172477 Adjacent sequences:  A261493 A261494 A261495 * A261497 A261498 A261499 KEYWORD nonn AUTHOR Alois P. Heinz, Aug 21 2015 STATUS approved

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Last modified November 26 22:15 EST 2020. Contains 338651 sequences. (Running on oeis4.)