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A115562 a(n) = number of distinct squarefree ternary (cyclic) sequences uniquely containing every possible length-n substring. 0
2, 3, 0, 6, 0, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Sometimes called "squarefree de Bruijn sequences" Two such sequences are distinct if they are not cyclic permutations of each other. Open: do any such ternary sequences exist for n>4 ?

LINKS

Table of n, a(n) for n=1..10.

EXAMPLE

a(2) = 3 because the following 3 sequences contain each length-2 substring {01,02,10,12,20,21} while avoiding any square {00,11,22} and are all distinct from each other:

010212

012021

012102

CROSSREFS

Sequence in context: A122830 A321296 A190902 * A127468 A173720 A173717

Adjacent sequences:  A115559 A115560 A115561 * A115563 A115564 A115565

KEYWORD

hard,nonn

AUTHOR

Jim Nastos, Mar 11 2006

STATUS

approved

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Last modified May 7 20:36 EDT 2021. Contains 343652 sequences. (Running on oeis4.)