OFFSET
1,3
COMMENTS
Permuting the alphabet will not change a word structure. Thus aabc and bbca have the same structure. This is identical to A000740 for n>1.
REFERENCES
M. R. Nester (1999). Mathematical investigations of some plant interaction designs. PhD Thesis. University of Queensland, Brisbane, Australia. [See A056391 for pdf file of Chap. 2]
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..500
FORMULA
a(n) = Sum_{d|n} mu(d)*A000225(n/d-1) where n>0.
G.f.: Sum_{k>=1} mu(k) * x^(2*k) / ((1 - x^k) * (1 - 2*x^k)). - Ilya Gutkovskiy, Apr 15 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
Terms a(30) and beyond from Andrew Howroyd, Apr 15 2021
STATUS
approved