OFFSET
1,1
COMMENTS
a(n) is also the number of permutations of [n+1] realized by the binary shift. The binary shift is the operation (w_1,w_2,w_3,...) -> (w_2,w_3,...) on infinite binary words. The relative order (lexicographically) of the first k shifts of a word, assuming they are all different, determines a realized permutation of length k. [Sergi Elizalde, Jun 23 2011]
Also, sum over A059412(1..n), hence number of ultimately periodic binary sequences uvvvv... with |u|+|v| <= n. - Michael Vielhaber, Mar 19 2022
REFERENCES
M. Domaratzki, D. Kisman, and J. Shallit, On the number of distinct languages accepted by finite automata with n states, J. Autom. Lang. Combinat. 7 (2002) 4-18, Section 6, g_1(n)
Cyril Nicaud, Average state complexity of operations on unary automata, Math. Foundations of Computer Science, 1999, Lect. Notes in Computer Sci. #1672, pp. 231-240
Jeffrey Shallit, Notes on Enumeration of Finite Automata, manuscript, Jan 30, 2001
LINKS
Sergi Elizalde, The number of permutations realized by a shift, SIAM J. Discrete Math. 23 (2009), pp. 765-786; arXiv:0909.2274 [math.CO], 2009.
FORMULA
sum(psi(t)*2^(n-t), t=1..n), where psi(n) is number of primitive words of length n over a 2-letter alphabet (expressible in terms of the Moebius function).
Hence, a(n) = 2*a(n-1) + psi(n), with a(0)=0 or a(1)=2.
EXAMPLE
a(1) = 2 because there are exactly two languages accepted by unary DFA's with 1 state. Also, because both permutations of length 2 are realized by the binary shift: the word 01000... realizes 12, and the word 1000... realizes 21.
MAPLE
A059413 := proc(n)
add(A027375(t)*2^(n-t), t=1..n) ;
end proc:
seq(A059413(n), n=1..10) ; # R. J. Mathar, May 21 2018
MATHEMATICA
a[n_] := Sum[DivisorSum[k, MoebiusMu[k/#]*2^#&]*2^(n-k), {k, 1, n}];
Array[a, 30] (* Jean-François Alcover, Jul 10 2018 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Jeffrey Shallit, Jan 30 2001
STATUS
approved