Permutations: Adjacent Elements Are Coprime
Leroy Quet
qq-quet at mindspring.com
Mon Mar 28 19:43:49 CEST 2005
I wrote to seq.fan about this a while back, perhaps, but I cannot
remember what kind of replies, if any, I received.
Could someone calculate/submit the sequence, if it is not already in the
database, where the nth term is the number of permutations of
(1,2,3,...,n) where each integer is coprime with its closest neighbors in
the permutation.
I get, by hand (so I might have made a mistake), the sequence beginning:
1,2,6,12,72,68,...
For example,
for n = 6, we can have in the count the permutation
5,4,3,2,1,6,
but not the permutation
2,5,4,1,6,3
(because here 3 is adjacent with 6).
thanks,
Leroy Quet
More information about the SeqFan
mailing list