OFFSET
1,1
COMMENTS
A word is primitive iff it is not a power, i.e., repetition, of a subword. The only non-primitive words with a prime number of letters (here: digits) are the repdigit numbers. Thus, the first nontrivial terms of this sequence are 1010,1212,...
This sequence does *not* contain all non-primitive words over the alphabet {0,...,9}, namely, it excludes those which would be numbers with leading zeros: 00,000,0000,0101,0202,...
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
MAPLE
F:= proc(d) local p, R, q;
R:= {seq(x*(10^d-1)/9, x=1..9)};
for p in numtheory:-factorset(d) minus {d} do
q:= d/p;
R:= R union {seq(x*(10^d-1)/(10^q-1), x=10^(q-1)..10^q-1)};
od:
sort(convert(R, list))
end proc:
[seq(op(F(i)), i=2..4)]; # Robert Israel, Nov 14 2017
PROG
(PARI) is_A239019(n)=fordiv(#n=digits(n), L, L<#n && n==concat(Col(vector(#n/L, i, 1)~*vecextract(n, 2^L-1))~)&&return(1))
CROSSREFS
KEYWORD
nonn,base
AUTHOR
M. F. Hasler, Mar 08 2014
STATUS
approved