A115562 a(n) = number of distinct squarefree ternary (cyclic) sequences uniquely containing every possible length-n substring.

2, 3, 0, 6, 0, 0, 0, 0, 0, 0

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: A358276 A321296 A190902 * A343069 A127468 A173720

Adjacent sequences: A115559 A115560 A115561 * A115563 A115564 A115565

Keyword

hard,nonn

Author

Jim Nastos, Mar 11 2006

Status

approved