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A000011 Number of n-bead necklaces (turning over is allowed) where complements are equivalent.
(Formerly M0312 N0114)
27
1, 1, 2, 2, 4, 4, 8, 9, 18, 23, 44, 63, 122, 190, 362, 612, 1162, 2056, 3914, 7155, 13648, 25482, 48734, 92205, 176906, 337594, 649532, 1246863, 2405236, 4636390, 8964800, 17334801, 33588234, 65108062, 126390032, 245492244, 477353376, 928772650, 1808676326, 3524337980 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

a(n) is also the number of minimal fibrations of a bidirectional n-cycle over the 2-bouquet up to precompositions with automorphisms of the n-cycle and postcomposition with automorphisms of the 2-bouquet. (Boldi et al.) - Sebastiano Vigna, Jan 08 2018

REFERENCES

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

Seiichi Manyama, Table of n, a(n) for n = 0..3335 (first 201 terms from T. D. Noe)

Joerg Arndt, Matters Computational (The Fxtbook)

Paolo Boldi, Sebastiano Vigna, Fibrations of Graphs, Discrete Math., 243 (2002), 21-66.

H. Bottomley, Initial terms of A000011 and A000013

N. J. Fine, Classes of periodic sequences, Illinois J. Math., 2 (1958), 285-302.

Shinsaku Fujita, alpha-beta Itemized Enumeration of Inositol Derivatives and m-Gonal Homologs by Extending Fujita's Proligand Method, Bull. Chem. Soc. Jpn. 2017, 90, 343-366; doi:10.1246/bcsj.20160369. See Table 8.

E. N. Gilbert and J. Riordan, Symmetry types of periodic sequences, Illinois J. Math., 5 (1961), 657-665.

W. D. Hoskins and Anne Penfold Street, Twills on a given number of harnesses, J. Austral. Math. Soc. Ser. A 33 (1982), no. 1, 1-15.

W. D. Hoskins and A. P. Street, Twills on a given number of harnesses, J. Austral. Math. Soc. (Series A), 33 (1982), 1-15. (Annotated scanned copy)

Karyn McLellan, Periodic coefficients and random Fibonacci sequences, Electronic Journal of Combinatorics, 20(4), 2013, #P32.

F. Ruskey, Necklaces, Lyndon words, De Bruijn sequences, etc.

A. P. Street, Letter to N. J. A. Sloane, N.D.

Zhe Sun, T. Suenaga, P. Sarkar, S. Sato, M. Kotani, H. Isobe, Stereoisomerism, crystal structures, and dynamics of belt-shaped cyclonaphthylenes, Proc. Nat. Acad. Sci. USA, vol. 113 no. 29, pp. 8109-8114, doi: 10.1073/pnas.1606530113.

A. Yajima, How to calculate the number of stereoisomers of inositol-homologs, Bull. Chem. Soc. Jpn. 2014, 87, 1260-1264; doi:10.1246/bcsj.20140204. See Tables 1 and 2 (and text).

Index entries for sequences related to necklaces

Index entries for sequences related to bracelets

FORMULA

a(n) = (A000013(n) + 2^floor(n/2))/2.

EXAMPLE

From Jason Orendorff (jason.orendorff(AT)gmail.com), Jan 09 2009: (Start)

The binary bracelets for small n are:

n: bracelets

0: (the empty bracelet)

1: 0

2: 00, 01

3: 000, 001

4: 0000, 0001, 0011, 0101

5: 00000, 00001, 00011, 00101

6: 000000, 000001, 000011, 000101, 000111, 001001, 001011, 010101

(End)

MAPLE

with(numtheory): A000011 := proc(n) local s, d; if n = 0 then RETURN(1) else s := 2^(floor(n/2)); for d in divisors(n) do s := s+(phi(2*d)*2^(n/d))/(2*n); od; RETURN(s/2); fi; end;

MATHEMATICA

a[n_] := Fold[ #1 + EulerPhi[2#2]2^(n/#2)/(2n) &, 2^Floor[n/2], Divisors[n]]/2

a[ n_] := If[ n < 1, Boole[n == 0], 2^Quotient[n, 2] / 2 + DivisorSum[ n, EulerPhi[2 #] 2^(n/#) &] / (4 n)]; (* Michael Somos, Dec 19 2014 *)

PROG

(PARI) {a(n) = if( n<1, n==0, 2^(n\2) / 2 + sumdiv(n, k, eulerphi(2*k) * 2^(n/k)) / (4*n))}; /* Michael Somos, Jun 03 2002 */

CROSSREFS

Cf. A000013. Bisections give A000117 and A092668.

The 8 sequences in Table 8 of Fujita (2017) are A053656, A000011, A256216, A256217, A123045, A283846, A283847, A283848.

Sequence in context: A222708 A120803 A284613 * A187213 A022476 A000013

Adjacent sequences:  A000008 A000009 A000010 * A000012 A000013 A000014

KEYWORD

nonn,nice,easy

AUTHOR

N. J. A. Sloane

EXTENSIONS

Better description from Christian G. Bower

More terms from David W. Wilson, Jan 13 2000

STATUS

approved

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Last modified July 20 08:26 EDT 2018. Contains 312802 sequences. (Running on oeis4.)