A324953 - OEIS

%I #7 May 24 2021 00:07:35

%S 1,54,2862,150690,7905894

%N Number of path change-ringing sequences of length n for 9 bells.

%C 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:

%C 1. The position of each bell (number) from one permutation to the next can stay the same or move by at most one place.

%C 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.

%C 3. The sequence must start with the permutation (1,2,3,4,5,6,7,8,9).

%C And does not satisfy:

%C 4. The sequence must end with the same permutation that it started with.

%C [*]: We define the length of a change-ringing sequence to be the number of permutations in the sequence.

%C 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.

%H Jonas K. Sønsteby, <a href="https://github.com/jonassonsteby/change-ringing">Python program</a>.

%H <a href="/index/Be#bell_ringing">Index entries for sequences related to bell ringing</a>.

%o (Python 3.7) # See Jonas K. Sønsteby link.

%Y 4 bells: A324942, A324943.

%Y 5 bells: A324944, A324945.

%Y 6 bells: A324946, A324947.

%Y 7 bells: A324948, A324949.

%Y 8 bells: A324950, A324951.

%Y 9 bells: A324952, This sequence.

%Y Number of allowable transition rules: A000071.

%K nonn,fini,more

%O 1,2

%A _Jonas K. Sønsteby_, May 01 2019