OFFSET
1,2
COMMENTS
See A056371 for an explanation of step shifts. Permuting the symbols will not change the structure.
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]
FORMULA
Use de Bruijn's generalization of Polya's enumeration theorem as discussed in reference.
a(n) = Sum_{k=1..4} A288620(n, k). - Andrew Howroyd, Jun 13 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved