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A056431 Number of step cyclic shifted sequence structures using a maximum of four different symbols. 4
1, 2, 3, 7, 7, 33, 29, 149, 245, 1230, 1665, 15973, 18199, 134482, 376433, 1415209, 2634597, 26534612, 33499359, 287002711, 727425501, 3332040944, 5794658931, 61120855045, 93825569009, 601444738252 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

See A056371 for an explanation of step shifts. Under step cyclic shifts, abcde, bdace, bcdea, cdeab and daceb etc. are equivalent. 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]

LINKS

Table of n, a(n) for n=1..26.

FORMULA

Use de Bruijn's generalization of Polya's enumeration theorem as discussed in reference.

a(n) = Sum_{k=1..4} A288627(n, k). - Andrew Howroyd, Jun 13 2017

CROSSREFS

Cf. A056412, A288627.

Sequence in context: A281909 A083809 A092967 * A281947 A199466 A199966

Adjacent sequences:  A056428 A056429 A056430 * A056432 A056433 A056434

KEYWORD

nonn

AUTHOR

Marks R. Nester

STATUS

approved

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Last modified March 8 20:14 EST 2021. Contains 341953 sequences. (Running on oeis4.)