A213969 List of primitive words over the alphabet {1,2}.

1, 2, 12, 21, 112, 121, 122, 211, 212, 221, 1112, 1121, 1122, 1211, 1221, 1222, 2111, 2112, 2122, 2211, 2212, 2221, 11112, 11121, 11122, 11211, 11212, 11221, 11222, 12111, 12112, 12121, 12122, 12211, 12212, 12221, 12222, 21111, 21112, 21121, 21122, 21211, 21212, 21221, 21222, 22111, 22112, 22121, 22122, 22211, 22212, 22221

Offset: 1

Author

N. J. A. Sloane, Jun 30 2012

Keywords

• nonn
• base

Comments

A word w is primitive if it cannot be written as u^k with k>1; otherwise it is imprimitive.

The {0,1} version of this sequence is

0, 1, 01, 10, 001, 010, 011, 100, 101, 110, 0001, 0010, 0011, 0100, 0110, 0111, 1000, 1001, 1011, 1100, 1101, 1110, 00001, 00010, 00011, 00100, 00101, 00110, 00111, 01000, 01001, 01010, 01011, 01100, 01101, 01110, 01111, 10000, 10001, 10010, 10011, 10100, 10101, 10110, 10111, 11000, 11001, 11010, 11011, 11100, 11101, 11110, ...,

but this cannot be included as a sequence in the OEIS since it contains nonzero "numbers" beginning with 0.

Lyndon words on {1,2}, A102659, are the numbers in this sequence which are also not larger than any of their rotations, i.e., in A239016. - M. F. Hasler, Mar 08 2014

References

• A. de Luca and S. Varricchio, Finiteness and Regularity in Semigroups and Formal Languages, Monographs in Theoretical Computer Science, Springer-Verlag, Berlin, 1999. See p. 10.

Links

• Robert Israel, Table of n, a(n) for n = 1..16222 (all terms with up to 13 digits)

Crossrefs

Cf. A213969-A213974.

Programs

Maple

P:= proc(d) local m,A;
    A:= map(t -> (10^d-1)/9 + add(10^s, s = t), combinat:-powerset([$0..d-1]));
    for m in numtheory:-divisors(d) minus {d} do
      A:= remove(t -> t = (t mod 10^m)*(10^d-1)/(10^m-1), A);
    od;
    op(sort(A));
end proc:
seq(P(d),d=1..6); # Robert Israel, Mar 24 2017

Mathematica

j[w_, k_] := FromDigits /@ (Flatten[Table[#, {k}]] & /@ w); L[n_] := Complement[ FromDigits /@ Tuples[{1, 2}, n], Union[ Flatten[( j[Tuples[{1, 2}, #1], n/#1] &) /@ Most[ Divisors[n]]]]]; Flatten@ Array[L, 5] (* Giovanni Resta, Mar 24 2017 *)

PARI

is_A213969(n)={fordiv(#n=digits(n),L,L<#n&&n==concat(Col(vector(#n/L,i,1)~*vecextract(n,2^L-1))~)&&return);!setminus(Set(n),[1,2])}
for(n=1,5,p=vector(n,i,10^(n-i))~;forvec(d=vector(n,i,[1,2]),is_A213969(m=d*p)&&print1(m","))) \\ M. F. Hasler, Mar 08 2014