OFFSET
1,2
COMMENTS
a(n) is the number of (change-ringing) sequences of length[*] n when we are looking at sequences of permutations of the set {1,2,3,4,5,6,7,8,9} that satisfy:
1. The position of each bell (number) from one permutation to the next can stay the same or move by at most one place.
2. No permutation can be repeated except for the starting permutation which can be repeated at most once at the end of the sequence to accommodate criterion 4.
3. The sequence must start with the permutation (1,2,3,4,5,6,7,8,9).
And does not satisfy:
4. The sequence must end with the same permutation that it started with.
[*]: We define the length of a change-ringing sequence to be the number of permutations in the sequence.
With this [*] definition of the length of a change-ringing sequence; for 9 bells we get a maximum length of factorial(9)=362880, thus we have 362880 possible lengths, namely 1,2,...,362880. Hence {a(n)} has 362880 terms. For m bells, where m is a natural number larger than zero, we get a maximum length of factorial(m). When denoting the number of path change-ringing sequences of length n for m bells as a_m(n), {a_m(n)} has factorial(m) terms for all m.
LINKS
PROG
(Python 3.7) # See Jonas K. Sønsteby link.
KEYWORD
nonn,fini,more
AUTHOR
Jonas K. Sønsteby, May 01 2019
STATUS
approved