

A000740


Number of 2nbead balanced binary necklaces of fundamental period 2n, equivalent to reversed complement; also Dirichlet convolution of b_n=2^(n1) with mu(n); also number of components of Mandelbrot set corresponding to Julia sets with an attractive ncycle.
(Formerly M2582 N1021)


72



1, 1, 3, 6, 15, 27, 63, 120, 252, 495, 1023, 2010, 4095, 8127, 16365, 32640, 65535, 130788, 262143, 523770, 1048509, 2096127, 4194303, 8386440, 16777200, 33550335, 67108608, 134209530, 268435455, 536854005, 1073741823, 2147450880
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OFFSET

1,3


COMMENTS

Also number of compositions of n into relatively prime parts (that is, the gcd of all the parts is 1). Also number of subsets of {1,2,..,n} containing n and consisting of relatively prime numbers.  Vladeta Jovovic, Aug 13 2003
Also number of perfect parity patterns that have exactly n columns (see A118141).  Don Knuth, May 11 2006
a(n) is odd if and only if n is squarefree (Tim Keller).  Emeric Deutsch, Apr 27 2007
a(n) is a multiple of 3 for all n>=3 (see Problem 11161 link).  Emeric Deutsch, Aug 13 2008
Row sums of triangle A143424.  Gary W. Adamson, Aug 14 2008
a(n) is the number of monic irreducible polynomials with nonzero constant coefficient in GF(2)[x] of degree n.  Michel Marcus, Oct 30 2016
a(n) is the number of aperiodic compositions of n, the number of compositions of n with relatively prime parts, and the number of compositions of n with relatively prime runlengths.  Gus Wiseman, Dec 21 2017


REFERENCES

H. O. Peitgen and P. H. Richter, The Beauty of Fractals, SpringerVerlag; contribution by A. Douady, p. 165.
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 = 1..3322 (terms 1..300 from T. D. Noe)
Hunki Baek, Sejeong Bang, Dongseok Kim, Jaeun Lee, A bijection between aperiodic palindromes and connected circulant graphs, arXiv:1412.2426 [math.CO], 2014. See Table 2.
R. Chapman, D. Knuth, Problem 11243, Perfect Parity Patterns, Am. Math. Monthly 115 (7) (2008) p 668, function c(n).
E. Deutsch and Lafayette College Problem Group, Problem 11161: Compositions without Common Factors, American Mathematical Monthly, vol. 114, No. 4, 2007, p. 363.
H. W. Gould, Binomial coefficients, the bracket function and compositions with relatively prime summands, Fib. Quart. 2(4) (1964), 241260.
R. Munafo, Enumeration of PeriodN MuAtoms
J. Shallit & N. J. A. Sloane, Correspondence 19741975
Index entries for sequences related to Lyndon words


FORMULA

a(n) = sum_{dn} mu(n/d)*2^(d1), Mobius transform of A011782. Furthermore, sum_{dn} a(d) = 2^{n1}.
a(n) = A027375(n)/2 = A038199(n)/2.
a(n) = sum_{k=0..n} A051168(n,k)*k.  Max Alekseyev, Apr 09 2013
Recurrence relation: a(n) = 2^(n1)  Sum_{dn,d>1} a(n/d). (Lafayette College Problem Group; see the Maple program).  Emeric Deutsch, Apr 27 2007


EXAMPLE

For n=4, there are 6 compositions of n into coprime parts: <3,1>, <2,1,1>, <1,3>, <1,2,1>, <1,1,2>, and <1,1,1,1>.
From Gus Wiseman, Dec 19 2017: (Start)
The a(6) = 27 aperiodic compositions are:
(11112), (11121), (11211), (12111), (21111),
(1113), (1122), (1131), (1221), (1311), (2112), (2211), (3111),
(114), (123), (132), (141), (213), (231), (312), (321), (411),
(15), (24), (42), (51),
(6).
The a(6) = 27 compositions into relatively prime parts are:
(111111),
(11112), (11121), (11211), (12111), (21111),
(1113), (1122), (1131), (1212), (1221), (1311), (2112), (2121), (2211), (3111),
(114), (123), (132), (141), (213), (231), (312), (321), (411),
(15), (51).
The a(6) = 27 compositions with relatively prime runlengths are:
(11112), (11121), (11211), (12111), (21111),
(1113), (1131), (1212), (1221), (1311), (2112), (2121), (3111),
(114), (123), (132), (141), (213), (231), (312), (321), (411),
(15), (24), (42), (51),
(6).
(End)


MAPLE

with(numtheory): a[1]:=1: a[2]:=1: for n from 3 to 32 do div:=divisors(n): a[n]:=2^(n1)sum(a[n/div[j]], j=2..tau(n)) od: seq(a[n], n=1..32); # Emeric Deutsch, Apr 27 2007
with(numtheory); A000740:=n> add(mobius(n/d)*2^(d1), d in divisors(n)); # N. J. A. Sloane, Oct 18 2012


MATHEMATICA

a[n_] := Sum[ MoebiusMu[n/d]*2^(d  1), {d, Divisors[n]}]; Table[a[n], {n, 1, 32}] (* JeanFrançois Alcover, Feb 03 2012, after Pari *)


PROG

(PARI) a(n) = sumdiv(n, d, moebius(n/d)*2^(d1))
(Python)
from sympy import mobius, divisors
def a(n): return sum([mobius(n/d)*2**(d  1) for d in divisors(n)])
print [a(n) for n in xrange(1, 101)] # Indranil Ghosh, Jun 28 2017


CROSSREFS

Cf. A000837, A003239, A008683, A008965, A022553, A034738, A035928, A038199, A051168, A054525, A056267, A059966, A143424, A167606, A178472, A216954, A228369, A294859, A296302.
Equals A027375/2.
See A056278 for a variant.
Sequence in context: A264686 A165729 A056278 * A161625 A234848 A300761
Adjacent sequences: A000737 A000738 A000739 * A000741 A000742 A000743


KEYWORD

nonn,nice,easy


AUTHOR

N. J. A. Sloane


EXTENSIONS

Connection with Mandelbrot set discovered by Warren D. Smith and proved by Robert Munafo, Feb 06 2000
Ambiguous term a(0) removed by Max Alekseyev, Jan 02 2012


STATUS

approved



